I was using Ubuntu as my primary OS for awhile but had to go back to XP because some of the software I need doesn't run under linux correctly.
Well I take that back...it would run correctly after hours of research, work, and probably breaking other things in the process. Simply got sick of all the issues I was having with it....
I love linux and still use it daily...but I doubt it'll be replacing my choice of Windows XP as my desktop OS anytime soon.