This version can read tags from protected AAC files (the ones you can buy on iTunes Store).
The Composer field has been added to the track properties: it's useful especially for organizing classical music. The ID3v2, Ogg Vorbis and Monkey's Audio parsers have been updated to read/write it.
Last but not least, you can now export tracks in the .m3u playlist format.
The most important new feature is the support for MusicBrainz: it allows to identify songs using a community-based database and to retrieve their meta data (author, album, title, track, year of release).
Another minor addition is the BPM field which has been added to the database. The ID3v2 parser now reads it as well, if present.