I would love to have a dedicated gaming PC, but that's a much more expensive and knowledge-intensive road to travel. The way I see it, there are two ways to go:
1) Buy a gaming PC from a Dell or HP or Alienware or whomever and pay a significant premium. On the good side the PC's all put together for me, comes within 10 days of my purchase, and has a nice warranty on all the parts. On the bad side, I've probably paid $2500, minimum, to get all that.
2) Put the PC together myself. It would save me about $1000, but I have to acquire all the parts and assemble them.
Unfortunately I don't really have the cash or the know-how for either option. I might be able to put a PC together with the help of a friend, but of course if a part breaks down (as they sometimes do) and my friend's not around, then I can't really fix it myself.
The 360 was the best option for me because there is so much out there. And now that I've spent some time with it, I think XBL is a fantastic service. (The jury is still out on whether or not it should be paid for, but that is another discussion, honestly.) I've always enjoyed PC games because of the multiplayer potential online. XBox and the PS3 have a robust player connection service, and each has games that really come to life in a multiplayer environment. The console/computer gaming lines are blurring.