I'll miss Ubuntu One. It was my unique cloud client. But it's time to move forward and if you have the Ubuntu One client installed you can remove with these commands (source):
sudo killall ubuntuone-login ubuntuone-preferences ubuntuone-syncdaemon mv ~/Ubuntu\ One/ ~/UbuntuOld rm -rf ~/.local/share/ubuntuone/ rm -rf ~/.cache/ubuntuone/ rm -rf ~/.config/ubuntu/ rm -rf ~/.config/ubuntuone/ sudo apt-get purge ubuntuone-* python-ubuntuone-storage* -y
RIP u1! FYI some alternatives with Ubuntu clients: Dropbox, Copy, Wuala, Bitcasa, Hubic or your Owncloud.