LAIRWARE  The developer has indeed taken you seriously. Hopefully 1.0.1 will fix this for you.  
(Version 1.0.1)

LAIRWARE  Corpsecorp: No worries, you can either turn off the feature, or use MPFreaker's handy artwork "Embed" button on any number of songs at a time, even your entire library.  
(Version 1.8b11)

LAIRWARE  MPFreaker 1.8 copes with the issue of iTunes-downloaded (unembedded) artwork, and now avoids overriding such artwork with new embedded artwork added by MPFreaker.  
(Version 1.8b9)

LEON MCNEILL  With iEatBrainz the default results can be quite off-the-mark, which requires a lot of care given that iEatBrainz replaces your song's title, artist, album, and track # all in one action. Fine if you really don't know for sure what a song really is, or don't know who sings it -- I myself use iEatBrainz for questionable tracks like that.

I know of no other solution other than MPFreaker which will automatically find and add artwork en masse to your library. Indeed, if you're happy with manually working with each song, all you really need is Safari and iTunes.  
(Version 1.2)

LEON MCNEILL  I have not heard of anyone experiencing corrupted tags since MPFreaker beta 3 was out, about five months ago. Unless I get some e-mail from you (or someone else experiencing some kind of tag corruption), I'll have to assume you're just trying to cause trouble, Mr. Anonymous.  
(Version 1.0b12)