Question: I use windows and now ubuntu and want to use ubuntu one to backup and sync files between them both so no matter what OS I use, I have the latest synced files. Is that possible?

Answer: 
Yes, there is [Ubuntu One client for Windows](https://one.ubuntu.com/downloads/windows/).
It is. You can install an Ubuntu One client in Widows (just follow the instructions on the Ubuntu One website), log in with your account and start syncing.