What everyone else said, plus (regarding the iPad app):
1) info about the number of albums in a focus
2) info about total playtime and time left in a playlist
3) sorting of artists by family name, as I believe is possible with the touchscreen MDMS. I want Nick Cave filed under C not N.
4) html like features in the review tab, with the possibility of hyperlinks

And regarding Control:PC:
1) it should look a lot more like Core Control, but in a web browser. I don't want to click four times to edit some metadata, and then click save.
2) you would expect it to give album info by double clicking on the album cover in the top left while playing music. But it doesn't.
3) the possibility of mass editing data. After ripping all my cds, I found that Nick Cave & The Bad Seeds were called simply Nick Cave. Correcting this should be a lot easier.
4) importing metadata from sources like last.fm, allmusic, discogs or whatever should be an option. This should not overwrite the metadata that is already in the system, but should be complementary.

MD600, MS600