I suspect anyone who uses the Ubuntu Operating System and needs this information already knows it, but the Ubuntu One online storage system will shut down on June 1st. All Ubuntu users should have gotten the email.
The Shutdown notice:
https://one.ubuntu.com/services/shutdown/
Ubuntu One is/was an online file storage service that was available free to Ubuntu OS users -- much like Dropbox. It offered 5 GB of storage free, with the opportunity to buy more storage, or earn more storage by referrals.
I have two laptops running Ubuntu 12.04 LTS, so I found it convenient to keep my work synched. It was accessible from Windows, but I never needed it for my XP desktop.
Dropbox is well supported on Linux, so that's the way I went. I'm sure there are other options.