Save the World... of Warcraft
Yup, I'm one of "those" people. I play World of Warcraft to pass the time if I don't have anything else scheduled to do. It's the only game I play right now, so it weighed heavily in my decision to upgrade to Vista. 
At the time, I was very happy to find that it ran without any troubles immediately after ugprading. But as I played, I discovered and eventually solved two issues:
First, after an hour of playtime, various objects would turn black. This was very annoying and made gameplay difficult. I guessed that someone had discovered this before me and would make a patch available to fix it. Since neither Blizzard nor Microsoft had a patch, I looked to NVidia --- yup, they had an updated set of drivers for my video card. Fixed.
Second, my framerate dropped from my marginal 20 fps to 15 fps. Ouch. The updated drivers didn't fix my framerate, so I looked at my resource usage. My disk is always hammered, but I ruled this out by finding a place in the game where it didn't have to load data. Second, I looked at other processes on the system. No programs were using CPU.
Since I wasn't constrained by CPU or IO, the graphics card must be the issue. On a hunch, I tried turning off Aero Glass (since this uses the graphics card) and my framerate jumped back to its old 20 fps. Now I only use WoW for a fraction of my computer time, so I didn't want to just leave it off. Looking around, I found the compatability tab. Here's what to do:
- Right click your WoW shortcut and choose "Properties"
- Click the "Compatability" tab
- Check the "Disable window composition" tab
Now when I play WoW, Windows will disable the glass effect automatically and restore it when I'm done.
Deductive reasoning FTW! Now if only they'd let me borrow the Sword of 1000 Truths....
-Ben Karas (aka Wristwatch on Medivh)