I spend an evening trying to get xmonad under OSX Mountain Lion to work, but with little success... I followed this guides (
http://www.haskell.org/haskellwiki/Xmonad/Using_xmonad_on_Apple_OSX#Modern_installation_instructions,
http://sourcematters.org/2012/06/27/xmonad-on-os-x-lion.html,
https://gist.github.com/3923233). I end up with having X11 configured as not run in Full screen mode, other wise nothing happens and I just see my normal OSX desktop. When I then start XQuartz app, I can start various xterms, or xlogo, or xman by pressing Mod-return, and switch to the default xmonad layouts, but don't get the idea how to manage opening other applications such as my browser or, for example, the Notes app.