I'm not seeing the Ubuntu One ribbon in Nautilus-Elementary. I have the nautilus-terminal extension as well, so I don't know if they don't work together.
I tried running nautilus from the terminal (for a separate issue), and I think I might be onto something. It seems the Ubuntu One ribbon is not finding something (it had an exception). I got the NE-Terminal working again by deleting the gconf directory for Nautilus.