I got the Vista beta 2 yesterday afternoon and installed it. It took almost 2 hours for it to install. So far I've only had 2 problems with it.
One was that the audio, that is installed onto the motherboard, wouldn't work. I tried several ways to get it to work but it still wouldn't. Luckily I still have my old computer so I took out the sound card I had in it, an Audigy 2, and put it in my computer and it worked after I installed the beta driver.
The second problem was the Windows Update. I got it to download the 2 updates pretty quickly, but when it came time for it to install it would just sit there for about 10 minutes still saying "Installing 1 of 2". I'd get tired of it stalling and I'd cancel the install. Its done that twice so far.
SL works fine in it after downloading and installing the Vista drivers from NVIDIA. It also seems to be a bit better fps wise and it seems to rez things a good bit quicker. Aero works even when I have Firefox up.
I haven't tried any of the games I have on my computer yet to see if they have any improvements.