Depends on what you buy and what you plan to play.
If you are into MMOs, top of the line PC now will last you three years for MMOs. With minor upgrades to ram and video cards thru those years.
If you are into the latest PC game that comes out every month at game stop etc... then it will get outdated a bit faster in the CPU and mother board areas.
When i was playing everyquest years ago, i wasnt a PC guy and only wanted one to play EQ. So i went to
www.cyberpowerpc.com and made up a basic stream lined PC for games. Good site for making up a PC for games only.