The only drivers I've had problem with under Win 7 are those for my Asus Xonar soundcard. Using the Win7 beta driver caused 32bit applications to stop working(!) and the Vista drivers wouldn't install due to a hard coded path that doesn't exist in 7. The answer was to extract the Win7 64bit drivers from the .zip and point the hardware wizard to that folder, it means I don't have the Asus sound mixer at the moment, but it sounds better (at certain frequencies) than the on board with the speakers I use.
FWIW, the RC disappeared from the MS site on August the 20th. I believe that you can still get keys from them (if not they are readily available on the 'net as there are only a handful).
As for Vista vs Win7, on rigs that ran Vista without any issues, it'll largely be a personal taste. I've not found it any quicker on the Q6600 with 4Gb RAM setup, but the laptop running a T2310 and 2Gb RAM is noticeably quicker to boot to desktop, is ready to be used as soon as at desktop and comes out of sleep almost instantly. MS have stated that Vista will be getting DX11 (yes, DX10 exclusivity was a ploy to get people to switch from XP).