Hehe it's vorbis, as ogg can also be theora and that would be a video format:)
And btw. support for ogg is far better then for mp3. mp3 is just more popular, as it's older.
EDIT: Don't convert files from mp3 to ogg, you may lose a lot of quality. If you have highquality or lossless samples compress them directly to ogg:)