I have seen KDE4 in action in Kubuntu and in OpenSUSE. It's a bloated pig, and I personally find the GNOME interface more intuitive. I might give it another chance soon, though.
EDIT: I don't know why I'm such a masochist. I really don't. I just installed KDE4 again, and yes, it still sucks. How do I even change the number of desktops? Right-click on the pager, "Configure desktops" set number of desktops to 4, click "apply" and... nothing happens. It stays at 2. It has always stayed at 2, every time I've tried KDE in three different distros. It should not stay at 2. I want 4 desktops, dangit, and even XFCE will do what I tell it (most of the time, at least, but it seems to suck at saving files). Also, KDE doesn't seem to play nice with Compiz- it screwed up a bunch of my settings, and Compiz generally just "feels" less smooth and well-integrated in KDE.
Much of this may be some prejudice, as I mostly use GNOME apps and a lot of them don't integrate well into the KDE desktop, making for an odd look... but even on native KDE apps or DE-independent stuff like FF and OOo, GNOME seems much better to me. And the menu layout for KDE is nonsensical.
On the plus side, it seems a bit faster now. However, this may be an illusion because I think I'm using Vista. Emerald has my aero-clone theme enabled, and the completely absurd mishmash of random and arbitrary structure behind the way KDE does things completes the illusion that I'm running Vista, and nothing can be slower than that.
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WAR IS PEACE
FREEDOM IS SLAVERY
IGNORANCE IS STRENGTH