Righty, I've had my FX6100 about a week now so I thought that, given that pretty much no-one anywhere on the 'net has done one, I'd give it a bit of a review.
I'll start by saying that if you want a high powered gaming machine with the best possible cpu then you should stop reading and click here. The FX can't compete with high end Intel stuff and I knew that when I bought it.
Price
I got mine when it was on offer from OcUk which, combined with the AMD cashback deal, put it at £92.99. With it's current price and the cashback it's £109.99. This puts it within a similar price bracket as the i3-2120, less than OcUk's single remaining Phenom x6 offering and almost half the cost of the 2500k.
First Impressions
The box is quite smart and everything's well packaged. The stock cooler's got a nice layer of thermal compound on the bottom and is very solid and chunky. The fan isn't overly loud and does seem to shift a decent amount of air for it's size. I can't comment on the stock cooler's performance as my chip went straight under water.
When first booted in a Gigabyte 990FXA-UD3 AMD 990X board paired with 8Gb Kingston HyperX 1600 RAM and a HD6950 it all loaded up first time with no issues. The ram needed a quick bios tweak to get it running at it's full speed but that was it. At stock it only pulled 1.232v.
Even though it's not the best money can buy from the first use it certainly felt faster than my Q6600 I was previously using and as those of you who have read my build log will know, it was anywhere between 30-200% faster depending on the application.
Performance
Time for some actual figures! All my comparisons have been dragged from anandtech's benchmark comparison tool as it seems to get passed around on the forums quite a bit. I've not been able to go to town and match every single benchmark they did as I didn't want to pay for software but I've done my best to download all the free stuff (I've used older versions to match the benchmarks) and used some software I already had.
I've used the i3-2120 as this is currently the FX6100's closest competition in terms of price. I've also included the 2500k as that's what everyone else has got
I've also included the FX at 4.8 (240x20) for a comparison of what it's capable of when pushed a bit. We'll get on to overclocking in more detail later.
First of all Cinebench and Bulldozer's arch enemy - Single Threaded Performance -
Beaten in to a bloody pulp by the i3 and the i5's just in a completely different league. Even overclocked it can't match a stock i3.
Multi-Threaded -
That's a bit better! A good lead over the i3 and not a million miles from the i5 when overclocked. Bulldozer does seem to love heavly threaded workloads.
Now for one of my most used pieces of software, Photoshop. I had to drop back down to CS4 to match the Intel benchmarks, it's even faster in CS5. This is time in seconds so lower is better. As I had to time it myself with a stopwatch I ran it 5 times, discarding the highest and lowest and averaging the remaining 3 times just to be as fair as possible.
Another win over the i3, still some way from the 2500k though.
Time for some more threaded work - encoding benchmarks. This is where Bulldozer really has a chance to shine.
The i3 with only 2 cores doesn't stand a chance here - the FX even managing to match a stock 2500k.
Again almost matching an i5 and leaving the dual core i3 for dead yet again.
And now the only game that I own that there was also a benchmark for - Dawn of War 2. Used the same settings as the benchmarks but I don't know what level they used so I used Fraps to get average FPS on the performance test tool.
Worse than an i3 at stock but pulls well ahead once overclocked.
As you can see from the above tests it really is shocking at single threaded applications but gains a distinct advantage over it's competitors once you start using more threads. An overclock really helps too, something that's not really possible on an i3.
Overclocking
I've got mine sat at 4.8 (240x20) at the moment and it's pulling 1.425v. It's a good, stable, overclock and as you can see from the performance tests it gives a good boost over stock speeds. It's the easiest chip I've ever had the pleasure to work with - you can pretty much just leave everything else stock and it's good for up to 4.6GHz before you need to change anything. Just increasing the multi will easily get you up to 4.8. And if you're not afraid of voltage and have a good cooling setup then this is possible -
It does pull a fair voltage when it's under load though, I had a tough time keeping temps under 60c!
It's also worth nothing that it scales much better if you raise the bus and not just the multiplier. Here's a quick Cinebench 11 benchmark to show the difference -
Conculsion
Is it a top gaming chip? No.
Is it a top encoding/workhorse chip? No.
Is it good on a budget? Yes.
Single threaded performance aside (because it's truely awful!) in most other cases it utterly destroys its nearest rival, the i3-2120. If you give it a little push it's not a million miles from the 2500k in modern applications. It'd be pretty naff if you tried to team it up with an SLI or Crossfire rig but I've not noticed any bottlenecking at 1920x1200 as most of the load gets lumped on the GPU. For ~£100 it's quite a good little chip.
The only issue is that the platform wouldn't give you the option to upgrade to a much more powerful cpu if you got bored (ie, i3>i5) and Piledriver's probably still not going to be anywhere near IvyBridge when it comes out.
I'll start by saying that if you want a high powered gaming machine with the best possible cpu then you should stop reading and click here. The FX can't compete with high end Intel stuff and I knew that when I bought it.
Price
I got mine when it was on offer from OcUk which, combined with the AMD cashback deal, put it at £92.99. With it's current price and the cashback it's £109.99. This puts it within a similar price bracket as the i3-2120, less than OcUk's single remaining Phenom x6 offering and almost half the cost of the 2500k.
First Impressions

The box is quite smart and everything's well packaged. The stock cooler's got a nice layer of thermal compound on the bottom and is very solid and chunky. The fan isn't overly loud and does seem to shift a decent amount of air for it's size. I can't comment on the stock cooler's performance as my chip went straight under water.
When first booted in a Gigabyte 990FXA-UD3 AMD 990X board paired with 8Gb Kingston HyperX 1600 RAM and a HD6950 it all loaded up first time with no issues. The ram needed a quick bios tweak to get it running at it's full speed but that was it. At stock it only pulled 1.232v.

Even though it's not the best money can buy from the first use it certainly felt faster than my Q6600 I was previously using and as those of you who have read my build log will know, it was anywhere between 30-200% faster depending on the application.
Performance
Time for some actual figures! All my comparisons have been dragged from anandtech's benchmark comparison tool as it seems to get passed around on the forums quite a bit. I've not been able to go to town and match every single benchmark they did as I didn't want to pay for software but I've done my best to download all the free stuff (I've used older versions to match the benchmarks) and used some software I already had.
I've used the i3-2120 as this is currently the FX6100's closest competition in terms of price. I've also included the 2500k as that's what everyone else has got

I've also included the FX at 4.8 (240x20) for a comparison of what it's capable of when pushed a bit. We'll get on to overclocking in more detail later.
First of all Cinebench and Bulldozer's arch enemy - Single Threaded Performance -

Beaten in to a bloody pulp by the i3 and the i5's just in a completely different league. Even overclocked it can't match a stock i3.
Multi-Threaded -

That's a bit better! A good lead over the i3 and not a million miles from the i5 when overclocked. Bulldozer does seem to love heavly threaded workloads.
Now for one of my most used pieces of software, Photoshop. I had to drop back down to CS4 to match the Intel benchmarks, it's even faster in CS5. This is time in seconds so lower is better. As I had to time it myself with a stopwatch I ran it 5 times, discarding the highest and lowest and averaging the remaining 3 times just to be as fair as possible.

Another win over the i3, still some way from the 2500k though.
Time for some more threaded work - encoding benchmarks. This is where Bulldozer really has a chance to shine.

The i3 with only 2 cores doesn't stand a chance here - the FX even managing to match a stock 2500k.

Again almost matching an i5 and leaving the dual core i3 for dead yet again.
And now the only game that I own that there was also a benchmark for - Dawn of War 2. Used the same settings as the benchmarks but I don't know what level they used so I used Fraps to get average FPS on the performance test tool.

Worse than an i3 at stock but pulls well ahead once overclocked.
As you can see from the above tests it really is shocking at single threaded applications but gains a distinct advantage over it's competitors once you start using more threads. An overclock really helps too, something that's not really possible on an i3.
Overclocking
I've got mine sat at 4.8 (240x20) at the moment and it's pulling 1.425v. It's a good, stable, overclock and as you can see from the performance tests it gives a good boost over stock speeds. It's the easiest chip I've ever had the pleasure to work with - you can pretty much just leave everything else stock and it's good for up to 4.6GHz before you need to change anything. Just increasing the multi will easily get you up to 4.8. And if you're not afraid of voltage and have a good cooling setup then this is possible -

It does pull a fair voltage when it's under load though, I had a tough time keeping temps under 60c!
It's also worth nothing that it scales much better if you raise the bus and not just the multiplier. Here's a quick Cinebench 11 benchmark to show the difference -

Conculsion
Is it a top gaming chip? No.
Is it a top encoding/workhorse chip? No.
Is it good on a budget? Yes.
Single threaded performance aside (because it's truely awful!) in most other cases it utterly destroys its nearest rival, the i3-2120. If you give it a little push it's not a million miles from the 2500k in modern applications. It'd be pretty naff if you tried to team it up with an SLI or Crossfire rig but I've not noticed any bottlenecking at 1920x1200 as most of the load gets lumped on the GPU. For ~£100 it's quite a good little chip.
The only issue is that the platform wouldn't give you the option to upgrade to a much more powerful cpu if you got bored (ie, i3>i5) and Piledriver's probably still not going to be anywhere near IvyBridge when it comes out.