Although I find it strange, Unity is usable. But last time I tried, Klipper didn't work with it, pretty much a deal breaker. I don't have an Ubuntu to test if the bug is fixed, but I googled and found the bug was reported exactly one year ago: https://bugs.launchpad.net/ubuntu/+source/kdebase-workspa... Reading that bug thread, I'm astonished at the Ubuntu folks' failure to take the last step to make the bug trackable, keep their user happy and thus pick the low hanging fruit:
Report the God Damn bug upstream on behalf of your user.
Some guy from Launchpad reacted very quickly and talked on IRC with a KDE developer about that bug, but came back and told the reporter: "go report the bug upstream" and closed the bug as invalid, when he could have spent 3 more minutes to report upstream. I don't want to offend the guy who tried to be helpful, but I find this sort of behaviour is irresponsible and amounts to shoving crap on your users' throat. The original reporter never reported back, and I would do the same if I would get this kind of crap.
An upgrading from Oneiric to Precise made the system unbootable. I think the room for improvement is huge, Ubuntu is a far cry from getting their act together.