Karmic Koala (didn't Boy George sing something like that?)
I did the update. So far, so good, mostly. For some reason, "switch user" in KDE is behaving as if I'd asked it to lock the screen. I did something stupid, i.e. put the 64-bit Flash plugin in the directory for 32-bit Firefox plugins, and that broke Flash on some sites in a bizarre fashion. Other than that, it's nice.