I worked on KDE 2.0, did some coding for KMail, and then because of time constraints from job and family had to give up on it. I quit using KDE soon after because I realized that other than one or two applications, I spent 90% of my day doing command line stuff. I used the BlackBox window manager for many years. Then, last year, I tried KDE 4.something again. Man, was I disappointed. The environment may have been nice and the look much improved, but very basic stuff was missing from a lot of the applications. Konqueror was hardly useable as a browser. There was no way to manage certificate and key stores, even using the dedicated application for that. Basic stuff that was there in 2.0 was simply missing. I don't know what discussions were had or what decisions were made since I left the community but someone seriously screwed the pooch on version numbering. To my mind, 4.4 or whatever I was using should have been a 4.0 pre-release. I got the impression that KDE's focus now is on the gee-whiz bells and whistles and they are less concerned with shipping something that works.
These days, I really don't give a crap about "desktop environment." I use the applications that I use, and again, I still spend a lot of my day writing command line applications to get real work done, mostly shuffling data from place to another or fixing problems created by user or programmer error. Frankly, KDE 4 felt like it was getting in the way, and its native applications (and I know some are written by the KDE team and some not) were lacking in features. I was forced to use applications that didn't integrate with the environment just to do something useful.
BTW, I feel pretty much the same way about Gnome, but I suppose that I am using Gnome since I switched from Kubuntu to Ubuntu. I really don't care, since the applications that I use don't integrate with any desktop environment.