Just setup a laptop with Ubuntu 10.10 and noticed that Ubuntu's offering a free cloud-based sync service with 2GB of storage. What protocols/methods does Ubuntu One support for connectivity? i.e. can I mount it as a block-device like Elastic Block Storage? SSH? More interested in using it for Ubuntu Server as a cheap off-site backup solution for Webservers, etc.
Ubuntu One is not a backup service, and I wouldn't recommend you using it for this.
Having said that, some people—some Ubuntu One hackers, in fact—do use it for this, but you have to know the limitations of the service in this regard (and I'm not going to explain them here).
Furthermore, you should be aware that dejà dup is going to be implementing “back up to Ubuntu One”, using our service as the basis for a backup system and not as a backup system per se. This I fully support.
Technically, Yes. However, as of the last time I used UbuntuOne, it was not encrypted, so I'd say no, to using it as a backup service. Also, most backup utilities run as a cron job, with elevated privledges. As such, the backup files are owned by root, which does not play nicely with the user type folders that UbuntuOne creates.
Definitely yes. The backup utility on Ubuntu (called "backup", but its real name is Déjà Dup) lets you store the backup to Ubuntu One. So even if you delete a file accidentaly, and the deletion is synced to U1, you will be able to restore the latest backup using the "backup" app.
You don't even need to open the app. Just right click on the file or folder you want to restore, and it will suggest "reverting" it.