The MusicBrainz service aims to become a community-driven replacement to CDDB, which your favorite MP3 encoder / CD player uses to pull down metadata for the CDs you stick in your computer. CDDB, as you’ve probably discovered, is full of errors, the metadata categories are limited, and results can be ambiguous. The CDDB API is also notoriously difficult to build apps around.
MusicBrainz aims to fix all that in two ways: 1) By using positive, unambiguous techniques to fingerprint specific tracks (imagine sending a friend a playlist file and it working on their computer even though the filenames, paths, and metadata are different), and 2) Letting communities collaboratively build metadata and enhance it over time via constant collaborative peer review, Wiki-style. Sounds a lot more capable than freedb.
This could become a beautiful thing. Or at least interesting to watch. Boing-Boing has more.