From LXF Wiki
The K Desktop Environment: hideously over-programmed, poorly designed, but it makes your screen look lickably good and has neat programs like Kate.
Uses Qt. Recently the developers have finally come to terms that they know little to nothing about GUI design, and are attempting to make reparations for this in future releases. The most popular example of bad design in KDE is the clock preferences panel, pointed out by GNOME's Nat Friedman in an interview.