I've been having a good deal of trouble with Ubuntu 1, on 11.something. Ubuntu One solidly occupies that perfect space where it is just barely stable enough to be useful, but not enough to be reliable. It is a space of peak frustration.
First, performance was terrible on my PC. I found the Ubuntu One daemon using 100% of the CPU. With a bit of Googling I found that this is a common problem - it just goes crazy for no reason. Ok... In attempting various suggested solutions, I found right off that the normal shutdown command for the sync daemon would not work. But this did:
sudo killall -9 ubuntuone-syncdaemon
I also did this:
u1sdtool -q rm -rf ~/.local/
Also, at some point in there I did what, I guess, re-sets the local Ubuntu One "marks on the wall".
rm -rf ~/.local/share/ubuntuone
In other interesting trivia, I also had Ubuntu One running on a Windows XP machine. This was not easy to install, but that's another story. The funny thing currently is that for the past 2 or 3 weeks, if I start the Ubuntu One GUI program on that machine, a dialog appears. It tells me that an update is available and asks if I want to upgrade.
At first I clicked "yes". But nothing further happens and it has never done anything, apparently, because the dialog continues to appear. So now I don't bother.