Following my disappointment with Kubuntu Lucid, I just got around to replacing it with the standard Ubuntu Lucid desktop. It's possible to switch desktop environments using a couple of package manager commands, but I decided to do a from-scratch reinstall.
With a little effort, I was able to make most of the Ubuntu desktop behave OK. Window management is still not up to par with KDE 3.5 + KStep window decorations, but it's enough for now. I'll probably switch my window manager to WindowMaker at some point. (NeXTSTEP-style window decorations with X11 window management gestures are the apex of desktop window management, for reasons that I could go into at length but won't today.) Visually, the new Ubuntu theme looks nice; in fact it looks and feels much better when you're using it than it does in screen shots.
However, there's one fly in the ointment. Sound didn't work. At all. Note that for all its flaws, Kubuntu, which is derived from the same base distribution, had no such problem, so it isn't simply a driver issue. I could bore you with all the details of my debugging adventure, but at the end of the day I blame PulseAudio, and Ubuntu's decision to make PulseAudio central to their desktop sound system. After a couple of hours of unproductive web searching and config file wrangling, removing the PulseAudio packages in Synaptic made sound work, sort of.
Yes, sort of. It still doesn't work quite right. When I open the System > Preferences > Sound menu, I get a dialog box saying "Waiting for sound system to respond" and nothing else. (This behavior occurred before I uninstalled PulseAudio, so that's not the cause.) Apparently a whole lot of people have run into variations of this problem since at least Ubuntu 9.10, and nobody seems to have definitive answers on how to solve it. I'd report it as a bug, but I suspect that it's one of those opaque symptoms with dozens of underlying possible causes and it's probably futile.
I want to emphasize that I haven't had a problem like this with a Linux distribution in years. This is literally a regression in behavior to Linux ca. 2005. Poking around by hand with .conf files in /etc just to get something working on my desktop is something I used to do. It's not something I expect to be doing in the year 2010.
So, anyway, I can't set my sound preferences. I guess I'll just have to cross my fingers and hope Ubuntu didn't assign any really annoying sounds to desktop events.