Now picard set compilation tag for every release that have not one artist for each track on album. But it's very strange for release like this http://musicbrainz.org/release/a5fc970c-0d2d-413c-a9f5-00df46dd3046 found it at compilations in iTunes instead "album artist" category http://img1.uploadscreenshot.com/images/orig/5/14907184927-orig.jpg
I suggest use compilation tag only for Various Artists releases. Or may be even better to check if all tracks on medium have in track artist field the album artist then not to use compilations.
I think it will be done when we allow to put (feat. ...) in track titles, but know it's strange to get compilation if album have only few tracks featuring with main album artist.
P.S. All major players (WMP, iTunes) group albums first of all by "album artist" tag, so we must understand that "TCMP - iTunes Compilation Flag (class 4)" is first itunes specific tag and as you can see at sreenshot above, the result it's not good. Also it affect to iPods. Think by what you start find my example album, i don't think that at first you look it at compilation, ok, but in artist list you don't find it
Alos iTunes Store albums like mine example don't have itunescompilation tag.