Updated to the new beta version of Kubuntu, because I heard they'd made some strides toward making KDE4 usable.
They have, but it still isn't.
I hate it, for a lot of reasons, most of which boil down to basic UI failures that I can't easily fix. (The active window's titlebar should not be gray; I should not have to change to a completely different, equally ugly theme to change this; I would like to be able to sort my programs by their names instead of their descriptions as I expect Firefox to be under "F", not "W".) In a nutshell, I use KDE not only because I really like the interface, but because the things that I DON'T like are easy to fix; KDE4 has an unpleasantly police-state simplicity where the only things I can do to customize my panel are change its position and its size. Not to put too fine a point on it, if I wanted a UI that I couldn't customize, I WOULD BE USING GNOME, NOT KDE, YOU DUMB BASTARDS.
Fortunately, Kubuntu's still shipping with KDE3 as its default. That should do just fine until KDE4 gets up to speed.
There are a lot of things to like about the KDE4 design, like the less-cluttered Launch menu, but it's just not worth all the annoyances.
Oh, and the instability, too. Firefox kept crashing. Though that may be because it's a beta; I'll have to work with it for awhile in KDE3 before I'm sure.
EDIT: Most annoying thing about KDE3 at this point is that the update screwed up the volume keys on my keyboard. It took me over an hour to realize that there's nothing wrong with the keyboard settings, so it must be something wrong with KMix. (xev correctly returns XF86AudioRaiseVolume and XF86AudioLowerVolume, so X is receiving them correctly, and, weirder still, KMix sees the OTHER media keys, like XF86WWW and even XF86AudioMute, it just doesn't see the two buttons that it should be seeing as the fucking audio controller for some reason.) I remember having a bit of trouble with this when I first set Kubuntu up, but I don't have any bookmarks suggesting how I fixed it.
Pity; other than that Kubuntu's been great about recognizing hardware out of the box. (Oh, also I'm still trying to get the two extra buttons on my new mouse working. But I'm not trying very hard, as I don't need the damn things anyway. I have them set to each sword in The Witcher under Windows, and that's handy, but 3 are plenty for most of my day-to-day stuff.)