Whilst media players such as Rhythmbox are able to cope with the disc number metadata (and play tracks in the correct order), other devices/programs such as MP3 players which use sorted filenames play all the track ones, then all the track twos, etc.
With albums with multiple CDs I would like the track number vaules for the subsequent CDs to not start again at '1' but continue. This functionality would only be enabled when the value in 'disc' is greater than one. Then the previous CD's ripped files could be looked at to find the track number needed to start on.
http://bugzilla.gnome.org/show_bug.cgi?id=555433