mpd update has some important changes:
- together with the new plugin-like audio-driver architecture, the syntax of the config file is now changed. make sure to update your config file, or mpd will not start any more! an example file can be found under /etc/mpd.conf.example. additional explainations: man mpd.conf
- updating the db is now done only from the client-side. the mpd --update-db does not exist any more.
- OggFLAC support, Musepack support, Gapless MP3 playback, MP3 ReplayGain support and a lots more. for details go to the ChangeLog 0.12.1