Now that the featured artists guideline has changed to specify the use of artist credits rather than "(feat." in the title:

http://musicbrainz.org/doc/Style/Recording_and_release_group_titles/Featured_artists

we could have additional reports on http://musicbrainz.org/report for recording and release group titles which contain this string and need to be updated.

It also may be worth having a search for artists that contain this, although there are some legitimate ones.