While I think this question would need a little editing to avoid being an invite to a flamewar, I'll add some feedback:

  - I personally prefer linux (used to be Ubuntu, but now fedora or mint).
  - I used to prefer KDE and might be moving back in a few months when I get some better graphic card, although gnome 3 seems like a huge step in right direction.
  - I work together with people who love Macs, and I've been doing most of my paid work on a MBP for a couple of years. Still don't like it. Made me understand that usability is in the eye of the beholder.
  - Win 7 is great, but once you have to do a lot of the work in the terminal, it quickly becomes tiring. Also, getting a snappy setup on most prebuilt systems w/o reinstalling everything from scratch seems hard.