Re: Going Mad
You would need to tell the device not to synchronise that folder with U1 (I'm assuming it's outside of the Ubuntu One folder). I don't know how you do that with the Android app.
If the data is inside the Ubuntu One folder, you need to move it somewhere else. If you just move it, instead of copying it, it will delete what's on the server. Which will, in turn, delete what's on any other synced device, so make sure that's what you want before you do it.
Please, people, remember to BACKUP before you install that new system. Same if you're upgrading.