microsoft windows...not only for OS problems but also for ethical reasons:
*fsf.org
and coming to Linux(pardon other users,just expressing):
1)KDE is nice for most people i'd say.even i'm not here to bash it anyway,but as the thread starter asked.
i get irritated using it..may be its interface which i find difficult.GNOME works fine.
perhaps I think i'll find myself using it in version 4 of kde-kde4!
2)beep-media-player(winamp 2 like app made using gtk2) -it plays hide-n-seek with me when i minimize or maximise in GNOME.sometimes playlist manager is missing,sometimes equalizer windows hides..Ufff!
Linux users here,dont take my first comment to ur heart,its my personal experiance only.infact most people are using kde, ie near 50% share of DE in UNIX like Systems.