I've used KDE quite a lot. A like it, I really do. But the amount of small issues I have with compositing and caching that build up over time, regardless of distro, until after a few months I'm plagued by flashing and compositor crashes, or menus and file managers hanging for ages...it's just untenable. There are too many small bugs in too many nooks and crannies, and with KDE's scope (and scope creep), I'm not confident they'll ever be fixed.