I just upgraded our last machine to Kubuntu 12.04 (the laptop has been running it since a beta).  In place update with about 2 minutes offline... Debian/Ubuntu/Kubuntu really is amazing that way.

The new Kubuntu is pretty much just like the old Kubuntu.  It works, is very pretty, but just gets out of the way and lets me work.  There still appear to be some issues with disk i/o on encrypted disks (an slocate database update can max out your CPU inside the kernel so that it effectively hangs the machine until it finishes).  Haven't come up with a solution for that yet.  The KDE Telepathy mechanisms still seem a bit broken (e.g. try setting up an IRC connection on Freenode), but Pidgin works fine.

Not much else to say about Kubuntu 12.04.  A solid, practical desktop that looks great, comes configured fairly sensibly, has every feature you'd want (and more really), works on all the hardware I have, and has access to all the software I need.