Just a quick addition of another 2c (on this much covered topic)....
Although there is a preference for YADB, it is not the database that I have an issue with per se , it is the limited metadata. There is more out there now then just track name and genre. There is a world of fast changing and expanding data out there and it would be great if MC could help me harness it. (although it is worth mentioning that YADB had a low success rate with my father in-law's music, though that may have more to do with his bad taste and penchant for cheap compilations
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For example, I have been playing with MusicBrainz Picard and Lastfm. In this case, Last.fm and the musicbrainz database are correlated and if I know the musicbrainz song ID (from Picard) it can fetch information from the Lastfm api. From this, I can get information that I can't get in YADB (afaik), e.g. mood, similar artists, suggested playlists, alternate groupings, etc. This additional information (I am hoping) will help me re/explore my music and find tracks I have forgotten about.
Although it may be considered the realm of the plugin (or are there licensing issues?), I would really love this type of fetching of metadata from Last.fm and other sites to be a native feature of MC and for it to evolve over time as databases evolve. The lastfm DJ plugin is another good example of what I think should be a native part of MC, a tool that harnesses a big database to deliver music I either don't know or have forgotten.
One of the many reasons I like MC has been that there are very few things that can't be played with it (m4a, mp3, mkv, etc etc). It stays flexible and pragmatic. I would like this same type of freedom with where, when and why I get metadata. I would probably be happy to pay a supplement for a suite of metadata tools that helps me unlock a collection of music.
Craig