Does Ubuntu One work with Opera?
The ubuntuone.com web site will work with Opera in general. One known issue with Ubuntu One and Opera is when trying to setup the Ubuntu One client for the first time. During the "Add My Computer" process, Opera 9.5+ will give a security error message about a public web site requesting data from your computer. The only workaround for this currently is to set your default browser to Firefox in System->Preferences->Preferred Applications and then try restarting the Ubuntu One client to get through the authorization process. Once this step is completed, you can set Opera to be your default web browser once again.