MPfreaker is a handy app to have around for when you need to mass-tag files, but its fairly non-specific. the other comments make note that it's slow and cumbersome, it also often screws up since it relies on public DB's of albums that can often have conflicting genres, album titles, artwork, etc.

if the engine behind MPfreaker used some kind of parallel search requests, it would work better, perhaps by using the compilation/album title to pre-fetch data for the album before securing the artwork. it could then give you a choice on what album data to use, since not all albums are tagged properly by private or public users.

apart from the severe lack of speed and the tendency to butcher tags if you set it to overwrite (not recommended), the artwork collected is fairly broad and it works well, far faster than doing it yourself, though not as good as letting itunes do it for you.

in conjunction with a specific art viewer/fetcher to fix up the mistakes MPfreaker constantly and innocently makes, MPfreaker is a fine app.