Making a debut in the Karmic Koala release of Ubuntu (which I’ll post a more in-depth exploration of soon, I promise) is tight integration with the Ubuntu One cloud storage service, that is in no way similar to Apple’s MobileMe or Windows Live SkyDrive/Mesh. The most immediate difference between the former and the latter two services is that Ubuntu One has a nasty habit of not working at all.
The most common issue is that Ubuntu One won’t authorise your computer properly, and will therefore continue trying to add your computer to the list of authorised machines in an infinite loop. Mercifully, the problem is easy enough to fix, by removing the client software completely and then reinstalling it.
Quit the Ubuntu One client, then remove the authentication token from Passwords and Encryption Keys. (It’s also a good idea to move the Ubuntu One folder in your home folder out of the way.) The run the following commands:
$ sudo rm -rf ~/.share/local/ubuntuone
$ rm -rf ~/.cache/ubuntuone
$ rm -rf ~/.config/ubuntuone
$ sudo apt-get purge ubuntuone-client* python-ubuntuone-storage*
$ sudo apt-get install ubuntuone-client* python-ubuntuone-storage*
Everything should be working now: once you restart the Ubuntu One client, it should authorise the computer successfully.