Don't get me wrong, I do like the Xbox.. but I don't like it enough to actually own one.
Recently, I had to make the decision as to whether I was buying a PS3 or an Xbox. (I've already owned a Wii, I still believe the only thing they're good for is entertainment at Christmas.. and even then, most families would rather watch TV.)
The Xbox is undoubtedly superior where multiplayer gaming is concerned. The interface is a lot easier to use while in-game, and generally it's much less hassle to invite your friends to a game (or join one of theirs).
The downsides? Before the new Xbox console, you had to pay for an adapter. You could get away with hooking it up straight to your router if the planning of your rooms agreed, but for most, that wasn't an option. The adapter alone could cost up to (and sometimes beyond) £60.. Really?
Once you'd gotten over the shock of paying a substantial amount of money for a tiny black receiver, you're informed that if you actually want to play online with your friends, you need a Gold subscription. Yet more money that they'll drain out of your bank account. D:
I'll be the first to admit that multiplayer gaming on the PS3 feels more awkward to set up, but I can live with that. It's far superior in terms of single-player gaming, and if you don't always like gaming alongside random strangers, it's perfect for that. It can also double as a Bluray player (which I'll admit isn't much of a selling point for me personally, but it helped bring my parents around to the idea of helping me get one) and I feel that Sony's customer service beats Microsoft's in a heartbeat.
If your Xbox 360 is unfortunate enough to display the Red Ring of Death, Microsoft will assure you you'll get a replacement (providing you're covered by warranty or whatever). What they don't tell you is that they're sending you a used console.
If your PS3 becomes faulty through no fault of your own, Sony are kind enough to send you a brand new replacement model.
I may not exactly be an expert on these things, but I'll back Sony all the way before I back Microsoft.