Metadata Hootenanny is primarily a viewer/editor for the metadata contained in quicktime movies (in QuickTime Player they are referred to an Annotations, and are editable (awkwardly) in the Get Movie Properties menu item in Quicktime Player Pro).  It uses the quicktime framework for anything more impressive than manipulating strings.  It is written in Objective-C.  The layout is your basic iTunes style (sans brushed metal).  There's a big table that displays the movies and their metadata, in which you can sort, search and edit the data.  I can't compare it to other programs which access QT metadata, because I know of none besides QTPlayer itself.  The advantages over that are (1) price (2) ease of use.  with qtplayer you can't compare different movies by metadata, editing any metadata is a major PITA (you can't even cut/copy/paste in that window), and you can't search it by any means.

There's also an option to look up data on IMDB.com and EPGuides.com if your movie is a DVD rip or a TV capture.
Peripheral features include: (1) add/edit/delete/search Quicktime Chapter tracks (2) movie playback, with such features as Fullscreen, Playlist, Shuffle, and remembering your place in a movie when you go back to it (3) Fix sound sync (4) save database to tab-delineated (spreadsheet-compatible) text file, useful for things like movie size, duration, dimensions, video and audio format (at least I know I already had a spreadsheet of these things for my simpsons rips, and that was a lot more work to compile).
Planned features include: (1) limited authoring of wired movies to do menus a la DVD interactive menus, for switching sound tracks and subtitles, and scene selection (hopefully I can let you pick your frames from the movie to create the scene selection menus) (2) more information about the movie like video/audio bitrate, framerate, etc.