Theora scales from postage stamp to HD resolution, and is considered particularly competitive at low bitrates. It is in the same class as MPEG-4/DiVX, and like the Vorbis audio codec it has lots of room for improvement as encoder technology develops.
Theora is in full public release as of November 3, 2008. The bitstream format for Theora I was frozen Thursday, 2004 July 1. All bitstreams encoded since that date will remain compatible with future releases.