Update:

I kept it for 3-4 days until I realized that 400+ dollars on another game machine when I already had a good computer was pretty frivolous.  The 360 has some very cool features, but nothing really a PC can't do.  I was more impressed by the xbox live games than the actual 360 games.  Quake 4 for example looks much better on my PC than the 360, same with Prey.  I think that I would only recommend buying one if you can't afford a good gaming PC.

My PC specs;
Asus motherboard
AMD 3000+ 64 bit
1 gig dual channel ddr ram
nvidia 6800gs 256 ddr3
sounblaster x-fi
500w power supply