Comment My Experience (Score 3, Informative) 264
About a year ago I stuck a GTX 550 Ti in a machine that was at the time pushing five years old.
I generally upgrade video cards at least twice after the initial build of my computers, every 2 years or so. My needs for upgrading other components are generally low, because...really...who needs a top of the line processor? I generally stick to the top of the mid tier and it does anything I might need done for the next 5-6 years. As far as RAM goes, whenever I get a new motherboard I just put as much RAM as it supports in it, and have been known to spend more on RAM than CPU when building a computer.
I just recently rebuilt my computer (new motherboard, CPU, RAM, and a second GPU) for about $550, and that got it to a point where it can play Crysis 2 with max settings. I expect it will be able to play any game the makers throw at it for another two years before performance starts to become a real issue. Maybe longer, because it seems to me that game-makers are getting better at building games that still run (albeit less prettily) on older hardware.
If it hadn't been for some recent hardware failures I'd probably STILL be rocking the last machine, which would be over 6 years old now. I just didn't feel like throwing money down the drain buying a replacement motherboard that used and old-ass socket.
I think the only reason to buy absolute top-of-the-line hardware these days is to stroke your e-peen.