Ubuntu One is a Canonical cloud service that allows users to store, sync, and share their images, music files, contacts, and notes online, between computers, and mobile phone devices. For Ubuntu 11.04/11.10, you can start Ubuntu One from the Unity Launcher.
To uninstall Ubuntu One completely for any reason, then open the Terminal under Ubuntu (11.10/11.04/10.10) and run these commands:
sudo rm -Rf ~/.local/share/ubuntuone ~/.cache/ubuntuone ~/.config/ubuntuone
sudo rm -Rf ~/Ubuntu\ One/
sudo mv ~/Ubuntu\ One/ ~/UbuntuOne_old/``
sudo apt-get purge ubuntuone-client python-ubuntuone-storage*
Reboot now your system or log out the current session and log in back. If Ubuntu One icon remains empty in the launcher, then right-click it and select Remove From Launcher: