I have been using XP for years now (on my tablet for over 3) and it has been reliable. After lots of research and colleague input I decided to actually wait to upgrade my machine entirely so that I could avoid the entire vista fiasco (wasn't in the mood of paying more for a downgrade).

A buddy of mine has been using 7 as his main OS for a bit now and tells me it is greatly improved over Vista. I hope its true because I am not totally comfortable using Linux as my main OS and I would love to get a new Windows machine soon...