Plex simply identifies the file (local or networked) as video or audio and ignores all others. If it's a movie with the IMDB name (e.g., "Iron Man (2008)") then Plex will parse IMDB for the artwork, description, rating, etc. and download that info automatically. If you delete the movie, then Plex deletes this info automatically. It even works with the Apple remote (although I use a Harmony).
It does not integrate with iTunes' XML database, but I understand that is a future feature. So it's coming. I really miss it for music, but not at all for movies.
I just had a look at it, it just sounds too good to be true