I use Vista Ultimate on my primary desktop, Ubuntu server on my server @ home, XP PRo & Ubuntu on my laptop and ubuntu desktop on my second home pc.

I will say that I like the elevated permissions setup of Vista (posix ripoff) for security purposes but the rest of the o/s im not a fan of, and so im biased toward XP Pro still, although Ubuntu serves 99% of my daily needs perfectly. I find myself using linux more & and more everyday.