On my left I've got a Dell inspiron 531, ****ty (by comparison) amd64 dualcore 4400+, 3 gigs ram, nvidia 9800 gs, served up with a standard Dell tower case.
On my right I've got one i built myself, i7 920, 6 gigs ram, sapphire hd4870 vapor x, in an antec 900 case.
Not only is the Dell hotter, but it's also noisier, slower (obviously), attracts a lot of dust, and I would even go as far to say that it's uglier too.. even with the mismatched fascias of my dvd drives in the antec case.
I'm not going to say Dells are terrible, since it's not a fair comparison really.. the inspiron isn't a behemoth like my custom pc, it's also a couple of years old now, and it's running windows vista (*shudder*). Tbh, if you're going for a high performance pc, it's probably better and cheaper to cherrypick your parks and build your own.
I was actually going to claim that Dell is the cheap alternative until I decided to take a look at their site.. Essentially £2000 for what cost me less than £1000 to build myself.. sigh.