Vista was bad enough for me when it was released and is bad even with all the patches. I would never try a BETA / RC of a service pack that involves Vista.
This is what I have to say with my computer that has Vista:
Light Fuse, Get Away
Not to mention today it took me 35 minutes to extract a 11 MB zip folder. Other than that, the computer isn't that bad, but then again, I just haven't played enough with it.