I'm actually quite surprised at how well my current PC has aged. It's about as old as X360, and it's got 7800 GT in it (which was released even before the 360, probably making it an equivalent of Geforce 3 in Xbox era), and it can still run the newest games at about the same level (performance and visuals) with X360 games (Oblivion, UT3, BioShock, Lost Planet), or even better in some games (C&C 3, HL2:Episode 2). I haven't upgraded my PC since then (as I kind of stopped gaming the whole 2006, and just recently started to play games again). So much for upgrading once in a month to keep up with consoles.
I think what most people forget when comparing performance between PC and Xbox 360 is that, you have to run your game at 720p instead of the uber resolutions such as 1920*1080, or 2560*1600. People are complaining that their 2-year-old PC can't run games at their native monitor's resolutions as well as Xbox 360 at 720p. Well, duh! Obviously you can't expect your old PC to run games smoothly at those resolutions (I would love to though), but it's not really an apple-to-apple comparison. Obviously an old PC would run games worse than Xbox 360 at resolutions that are pushing about twice or thrice as many pixels as 720p...