Reader Scott kindly dropped us a note (thanks!) that Nvidia released new drivers for Windows Vista on Tuesday, and hidden in the release notes is a note that the "low frame rates" within WoW have been fixed.
So if you're running WoW in Vista, have an Nvidia graphics card (with one GPU), and still having graphical problems, a driver update definitely wouldn't hurt. Things seem to have calmed down on the graphics issues since a few patches have hit, but maybe there are still a few of you out there looking for a solution.
As for us Windows XP users, looks like we're still stuck with an older driver version. If you've updated your drivers on XP and are still having problems, the best thing to do is probably just to let Blizzard know about it.
Update: Whoops, Slashrude (and other commenters) point out what I missed: these are beta drivers, which means installing them may not be such a good idea. Update at your own risk.