Mine arrived today....!
This thing is awesome, really. I looked at it a couple of weeks ago and thought "what's the point in that?", then last week I was thinking "is it really that good?".... then I bought one. My CPU (Phenom II X3 720 BE @2.8GHz) runs very cool anyway; with the AMD stock cooler it was about 35/55 (idle/load, in degrees C).
Installation was... well it would have been easier if a) I wasn't ludicrously clumsy and b) the instructions had bothered to tell me the backplate I already had installed from the AMD stock cooler worked fine.... it was annoying disconnecting and removing the motherboard only to discover there was no reason to make the swap. Also, I found it completely impossible to install as shown in the various videos - the retention ring is not far enough from the chip surface even with the screws as loose as possible without it actually coming off again. I couldn't get the thing in, so I attached the ring directly to it then just held the whole thing in place while I screwed it down tight.
Also, the layout of my motherboard is just nuts. God knows who decided all of the fan connectors (save CPU fan) had to be either in the bottom left or bottom right of the board. The pump power cable just reaches, going down to the bottom left through the gap between the graphics card and the board... any further and it would be under some tension. I'm glad it's not, as the connectors are hardly what you'd call sturdy (on the motherboard, I mean - it's just three pins).
Anyway - as a cooler, this thing rocks. I have an Antec 900, so I removed the tricool fan from the rear 120mm mount and replaced with the single corsair fan and the radiator. It's currently an intake, with the radiator on the inside (so push configuration).
Idle temperatures are around 14 degrees, rising to around 21-23 degrees under load. That's pretty much begging for a massive overclock...
This is all with the fan at about 1200 RPM too. Not managed to get the temps up enough for it to increase the speed!
Noise-wise; the stock (corsair) fan is pretty darn quiet. I can't tell it apart from the tricool case fans, which are all set on low (so pretty much the same speed - 1200 RPM according to the manual) and the PSU fan (which is a whisper quiet Antec Neo HE 430W). Compared to the stock cooler, the H50 is essentially silent, as I had to remove a nearly identical 120mm 1200 RPM fan to install it. The pump is very quiet, at least where I'm sat (about 4ft away). It seems to be quiet a low whirring sound - I was expecting something much more intrusive and high-pitched. I suppose it's because it's immersed in liquid, rather than air?
Anyway - this product gets 5/5 from me. It gives incredibly low temperatures, it's quiet, it was relatively easy to install (compared to the nightmares I've had installing GPU coolers) and its pretty cheap - a bit more than a decent air cooler perhaps, but it's much smaller and it doesn't matter that my GPU is venting hot air directly upwards any more, which means I can replace the noisy HD4770 cooler with my trusty TR HR-03 and 92mm red wing...
Thanks to everyone on this forum who helped me make my decision to buy this, especially those who posted shots of their setup - they were really useful!!