I realised today when signing in, that everytime i use my computer I send some data back and forth to the Ubuntu One service, for obvious reasons, and that would actually mean Canonical could save us users data, like when we use our computers and how, and (if the Ubuntu One-folder on the server ain't encrypted in a good manner) what content we want to save in the cloud, and since Ubuntu One is not open source, we, the community, can't check if Canonical logs more than we are comfortable with.
Don't get me wrong, I'm no conspiracy nut, just courious :).
Best Answer
UbuntuOne's client is licensed under GPLv3. That means the client (ubuntuone-client) shouldn't be sending any usage information to Canonical. However, the server side code is closed, so there could be some statistical tracking.
The website is using Google Analytics both when you're logged in and when logged out.
The privacy policy states that your personal information won't be shared "except to provide you with services, comply with the law, or protect our rights" and isn't even stored "unless required for the on-going operation of our services".