Here is one way to store your stuff more securely in the Ubuntu One cloud.

0) If you mess up and need to start over again follow these directions to completely remove Ubuntu One and start again.

1) Install the file encryption program Cryptkeepter with sudo apt-get install cryptkeeper at the shell, or your favourite package manager. This uses an encrypted file system called EncFS for pass-through file encryption - essential for having your stuff be readable to you but gibberish to anyone else.