If I attempt to run Picard by double clicking the icon, it fails to open. There's a dialog box which says "MusicBrainz Picard Error" with the options "Open Console" and "Terminate". If I open Console, I see:

04/06/13 13:50:31,059 MusicBrainz Picard[8354]: MusicBrainz Picard Error
04/06/13 13:50:32,433 com.apple.launchd.peruser.501[119]: ([0x0-0x2e02e0].org.musicbrainz.picard[8354]) Exited with code: 255