Looks like Vista SP2 (service pack 2) may be coming out by the middle of 2009. Of course, by then the buzz might be so strong about Windows 7 that people may not care about Vista very much.
I've been running Vista on several different PCs and I prefer it over XP when I'm using a tablet. Otherwise, XP runs just fine and uses less resources. I'm anxious to see how Windows 7 will run on my UMPC and tablet.
Meanwhile, I'm also testing Ubuntu and Mac OS X. When Apple comes out with a really nice looking tablet or UMPC, I may go back to Mac. I miss the old days with my Apple Newton MP2100.