Just an idea, not sure if you'd want to do it for copyright reasons.
The main sites with the cd covers on them however dont seem to have been attacked so there doesn't seem to be too much of a problem with cd covers being provided online.
Ask users if they mind sharing their cover art with other users. Then Either do one of two things. Create a centralised MJ db of covers that is stored on the MJ servers and set it so that MJ can get covers from its own server before trying to get it from whereever it gets it now. Or the other idea is to just collect a db of what covers users have, if someone requests a cover then the message is passed on to the user who has the cover via MJ, MJ then replies to the user who wants it with the cover - all fully automated. This would save users having to use up loads of bandwidth uploading all their covers.
It would also save MJ from having to use up bandwidth hosting the covers.
It would be a great feature though.
It'd be unique to MJ which would give it an edge over all the other programs as people would have to login to MJ to get the covers from the MJ db so it would make them use MJ.
This could be extended even further to create a lyric's db too which would automatically get lyrics from songs from a central MJ server which was updated from the users automatically - obviously with their permission to participate.
Both of these would make MJ a must have if people wanted a program that could make the mp3's as complete as possible
One last idea - this could all be taken a step further, it would require more effort and is a much bigger step but the music industry must have all the lyrics and cd's it ever makes on computer. It could EASILY be set up so that every time a new album is made, the cd industry automatically passes this info onto a large cddb so that it's all filled in fully correctly, the moment the album is released automatically and doesn't require users to do it.
The same again with the lyrics and cover art for that matter.
It would require a deal to be struck up with the music companies obviously and would require some programming work to integrate that part of their db's that contained the information into a centralised db but it'd be WELL worth it for whoever did it I'd imagine in the long run.