No, don't upgrade. Long answer: Windows 8 does present a few problems here and there, and it definitely wasn't worth it for me. I use Windows only for gaming, and now I have to run my games in compatibility mode to still get triple buffered sync via d3doverrider (an absolute must for me). Unfortunately compatibility mode prolongs level loading times many times over, having to wait for several minutes while the game is loading the next level. This doesn't affect all games, but it happened to the games I play the most.
The difference in gaming performance is negligible, so no, I wouldn't upgrade.