We have an XLS file that has been corrupted (we use LibreOffice and it appears that some sort of corruption has taken place). The corrupted file then synced to U1. Is it possible to rollback or restore earlier versions of a synced file?
As of January Ubuntu One doesn't have built-in versioning.
I haven't seen anything to the contrary, so I assume this is still the current state of things.
As the other answer there suggests, if you need versioning, you can use a version control tool like Bzr or Git to keep version histories of all your files and sync these with U1 too. Provided you used the VCS properly, this would give you a nice system for rolling back changes.
If you want to know as soon as U1 gets versioning, I suggest you subscribe to their twitter feed.