I have been using Windows/Linux. Tried Mac for few months, at that time I was not very impressed but it was an old machine. Mac is excellent in terms of stability. Sometimes I do feel like trying out the latest ones.
I use vista only to play AOE3.

(and do some other stuff). I have some strong views on windows but as Lil Chris said, no point is starting a flame war.
I am all for Linux. The only con about using Linux is sometimes you don't have the time to play with it. If you want to get things done quickly, it can be frustrating to look for solutions, trying them out and so on. On the plus side, no viruses and stable as a rock.