The standard audio-format for music in Rhythmbox is Ogg. For some reason none of my music encoded as OggVorbis shows up in the Ubuntu One Mobile Music application on my Android phone. The MP3s do show up. It looks like the Ubuntu One servers are not indexing Ogg-files, although it is THE open format for music with superior quality to MP3 and Ubuntu's Rhythmbox encoded my CDs to that format. Solution?
We've just released ogg support on devices that support it (Android, Ubuntu).
There are 2 things that held back ogg support in our first release:
We also surveyed mimetypes of our existing users, and only a very small percentage of people had ogg files (I do understand the chicken-and-egg situation).
Ubuntu One Mobile only currently supports the streaming of MP3 files, but may support open codecs like OGG and FLAC in the future.
Source: https://wiki.ubuntu.com/UbuntuOne/FAQ/WhatAudioFormatsAreSupported