I use Ubuntu 12.04.
My files is small but I can't shutdown computer if Ubuntu One is syncing even when I force shutdown. That mean When I clicked on shutdown button on the panel, System asked me: Ubuntu one is syncing, can't shutdown...Lock screen | cancel | shutdown anyway ----> I clicked on "shutdown anyway". Then shutdown screen appeared and It was counting 1,2 dot but stopped right there. Even 1 hour after, nothing is changed.
I don't know why if it is not syncing, I can shutdown computer easily. So, a friend of mine also has the same issue.