What other Desktop Environments are making usability improvements that KDE (overall) is not making?
Windows 8 is an unmitigated user experience disaster with a boatload of functionality that is hidden and non-obvious.
OSX Mountain Lion is part 2 of making OSX more like iOS, dumbing down the desktop environment to make it "idiot friendly".
Gnome Shell/Unity/Whatever other crappy forks are making the same mistakes as both Windows 8 and OSX.
It seems to me that KDE is the only mainstream DE that will, in the future, be usable at all. Up to now, they haven't made any concessions to the user experience just because they wanted to be "modern" or "forward thinking". Also, since 4.4, KDE has gotten significantly better and more stable, in my opinion. The design has been cleaned up a lot, and little functionality that I frequently use has been cleaned up and sped up. I keep using KDE because it is getting better and better with each release, for me.