You do realize that whatever you can do in iTunes you can do in Rhythmbox
and the Ubuntu One Music Store, right?
I have easily been able to sync my iPod Nano with RhythmBox. And what's more amazing: You can keep your songs! You don't have to wipe out the iPod to sync it with the RhythmBox library like you have to with a new iTunes library!
And here's the extra bonus: The Ubuntu One Music Store is DRM-Free, which means that you can burn as many CDs and sync as many iPods as you want. Also: RhythmBox comes prepackaged on the Ubuntu Live CD!!! As a result, you don't have to install it. It's already there!