I know at some point we had these fully divided (stuff composed by, stuff performed by etc) - but that was a bit of a mess since stuff was often in both places. It would be very nice to get a way to filter the list to only stuff where the artist is a writer, or only stuff where the artist is a performer (main use for me would be composer/pianists and composer/conductors, for an example see Leonard Bernstein where it's practically impossible to get a list of his compositions http://musicbrainz.org/artist/fa39bc82-9b27-4bbb-9425-d719a72e09ac/works )