It's been fine for me in Windows 7, I always used to get rid of the Apple auto updater, and I also never used to install Quicktime which was bundled with it, I thought it was fine for what I used it for, and in my opinion it was much simpler and much nicer to use than Windows Media Player.
It's absolutely brilliant in OSX though, I wouldn't use anything else, it does everything I want and it does it hassle free and quickly, I don't think it's ever slowed or crashed for me in Leopard or Snow Leopard.