I have been using 64bit Vista Ultimate since itsa MSDN release last year. (im still trialling it obviously )

First 6 weeks were shocking to say the least. But i persevered!!!!!

Now......all is great and i wouldnt go back to XP for anything.
Its looks good, feels smooth, seems stable, ALL my software/games run fine (except Nero, had to get newer version) and the driver support is great. (Runs system on the left)
It also networks well.