I tried KDE 4 back at the Fedora 9 Beta, I tried it again at the F9 preview release and will try it again at the final release (I plan to have it on a bootable USB pen drive, along with a GNOME one at the event we will hold locally for the release). But every time I end my test run quickly, after a few minutes.
I understand that KDE fans and users should be happy with it, the KDE SIG guys did a wonderful job, it looks polished and close to the default KDE look and feel (long gone are the controversial, good or bad, days of Bluecurve, RHL 8 and unified look and feel).
But longer I try KDE, the more displeased I get and more committed to GNOME. It looks alien to me, it feels alien to me. Yes, the desktop looks shiny, but all my shortcuts, reflexes and habits are useless here. I could train myself (probably in at least a few weeks of pain) and heavily customize to get something familiar but is much easier to stay with my current choices. Which does not means KDE 4 is a bad desktop, it just isn't the best desktop for me.