PC gamer here, so I know I'll get a shoe thrown at me for posting and all, but I couldn't help but pull this one out...
Macflash said:
A workable computer for gaming will run about 4-5 times what an xbox costs, a good one is even more,so it costs slightly more for computer gaming even though the games tend to be a bit cheaper. I personally have an xbox 360, because I don't want to spend more than $300 on my gaming system, and because I don't want to worry about getting a new video card/computer every other year because the games just got more cpu intensive.
So... you spend how much on a 360? Having never bought one, I can only go on the internet. Here's the first one that turns up on my usual shopping site: http://www.amazon.co.uk/Xbox-360-Console-Hard-Drive/dp/B001DTD0WM/ref=dp_ob_title_vg
Now, that's £350 for the console. I bought and built my PC, I spent around £600 for it, so far I'm £150 worse off than you. That console has a 60gb hard drive. Being as mine came with a 186gb HD, and I bought a Tera External (931gb of usable space), I'm better off for storing and installing games on my system.
But hey, ignoring the extra space I get, let's pick up on the other "strength" of the 360. The friends system you mentioned. To use that, you get to use Live. To use LIVE, you have to have to pay, meaning an extra £35 per year. I love that about consoles... You buy the console, you buy the game, you pay the phone company for the line, then you get to pay Microsoft an extra 35 quid for the privilage to USE said game on said console on said phoneline.
I take your point about upgrades and not being able to play stuff though, but if you build the PC right in the first place you're safe for 3-5 years before you need to upgrade.