"Listen offline and enjoy your favorite songs" anyone knows how to do that on an iPod Touch? I can't see any option for that.
I'm one of the developers of the U1 Music Streaming app for iOS.
@Frank is right. Currently, the only way to download music for offline listening is at the album and playlist level.
And I agree that it's not that intuitive. We have roadmap plans to improve the UI considerably, and in particular make it much easier to download music for offline use throughout the app.
I just struggled myself with figuring out how to cache songs for offline with the iOS version of the Ubuntu One Music app...
Start the Ubuntu One Music app. Go to 'Artists' or 'Album' and navigate to a song. There is an empty circle on the right side of the song. When you tab on this circle, it gets filled and the song is cached for offline use.
For whatever reason, the circle is not show in the 'Songs' view -- very unintuitive :-(
You can buy music directly in Rhytmbox or Banshee and then synchronize it to your iPod touch or mobile MP3-device just like imported music in library. Bought music in the Ubuntu One Store is DRM-free and can be burnt or copied to devices as often as you want.
See https://one.ubuntu.com/music/ for further reference.