Sadly all users of MPAD/MPOD share the same daily downloads limits to amazon and discogs, which for some maybe they will always experience that if the limit is reached early. Also the artwork isn't always correct, but at least MPAD always you to select alternates but that still isn't perfect especially when it can't find one.
Lately, i've been using an app called MusicBrainz
to download the cover art and save it as cover.jpg. You can configure it to just download the images and they usually have the alternate cover art when an album has multiple releases. For albums that it doesn't recognize, there are ways to add that information if you choose to do so.
You can also use MusicBrainz to fix your tags and even validate the tags by creating a fingerprint of the file and scan against the database. There are some limitations if you used a music manager (like itunes) where you won't be able to have it correct file names.
I think my biggest grip with the id3 tags, mpad and about every music player to date, would be with featured artists. I wish MPAD would respect the album artist tags and use that if it exists and not break out every artists. With the two options on how to sort the albums, none of them fully work and there really shouldn't be an option, it should just be a tab like albums, artists... so... albumartists tab would be very useful.