^Agreed.
If you want to "future proof" a build, the answer isn't more powerful components, but easy upgradability. I bough a HAF-X and a 750W PSU when I made my build, at the time both were unjustified. The case is massive and I didnt need that space, and 600W is more than enough for my single card. Could probably have cut down on both and gotten myself a 7950.
Then I buy a water-cooling loop, and suddenly my overkill case is useful. If I had bought a lower end case, wouldn't have been able to upgrade to W/C'ing without a new (and expensive) case.
PSU is the same thing. If I got a 600W, I would have to buy another PSU in addition to a graphics card if I ever want to Crossfire/SLI.