A simple, elegant (did I say free?) solution to all my missing artwork. No, the process is not automated, but I was able fill in the gaps on my large collection in one evening of obsessive fun. Just follow the instructions in the Help, que up your corrections and let'r'roll.

The only drawbacks I could find were the following:
1) If an album/cd is named "Greatest Hits" in iTunes, the artwork for every album named "Greatest Hits" (a fair number in my music) will all get the same artwork. My work around was to rename "Greatest Hits" (Bob Dylan) to "Bob Dylan's Greatest Hits" after highlighting all the tunes on the album, then using Get Info to rename the album. Then assign artwork.
2) If you que a list for processing, and theres a data error of some sort within the que, the error message you receive may not identify the faulty data well enough for lunkheads (like me) to readily identify the offending album to remove from the process que. Patience & working backward through the que, as well as que-ing a smaller number of albums in case there's a problem, took care of this issue (ie make your process que a smaller manageable number, instead of the huge one I created at first).

This program is great. I'm now enjoying my collection on a different level thanks to Artwork Assistant. Recommended.