I own an Xbox 360, my housemate a PS3 and we also both have PC's capable of moderate gaming (not quite Crysis level
It depends what type of gamer you are and how much you expect from your console. If all you want is to play the normal console games like racers, shoot-em-ups, rhythm games etc then the 360 serves well. The PS3, though potentially technically superior, is considerably harder to program for and so games on both platform run pretty much the same (infact some 360 games actually look better).
However the PS3 is a considerably better multimedia device. Its streaming capabilities work better and the blue ray drive does give it an advantage. It remains to be seen if the new 360 dashboard update will correct this but I wouldn't bet on it. Pretty much every big game is coming out cross platform now so its games catalogue is expanding fairly rapidly. Biggest downside as far as the PS3 is concerned is the price, which can only be justified if you are actually going to make use of those extra multimedia features.
As usual the PC is the best option for the "hardcore" gamer, especially with the "games for windows" initiative on Vista bringing the online experience and peripherals from the 360 where appropriate. Plus on the occasion when I actually have to get some work done its nice to have a PC with good specs so I can do silly things like run 5 virtual machines from memory simultaneously.
Overall I decided on a combo of Xbox 360 core system for "casual" gaming and a midrange PC (built myself, components circa £300) for strategy/fps and work. Doesn't cripple the finances and covers most if not all of the bases.
Just my 0.02p