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: 
I believe it should be possible.

Just install [Ubuntu One](https://one.ubuntu.com/downloads/) on both Windows and Ubuntu.

Say you have a folder `Documents` in Ubuntu and you want it to be synced between Windows and Ubuntu. Then just select Sync Locally for that folder in both the Ubuntu and Windows - Ubutnu One Client.

![enter image description here](https://i.stack.imgur.com/TYfFB.png)
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.