With the 11.10 update, I discovered an "Ubuntu One" address book in my Thunderbird address books. Exciting! But ... it doesn't seem to be syncing. I've got "Enable Contacts Sync" checked in Ubuntu One's control panel and I'm able to add addresses to the new "Ubuntu One" address book, but they don't seem to leave my laptop.
I don't see any way to troubleshoot this within Thunderbird or Ubuntuone.