NEW: Re-Embed Artwork
I got suspicious when I received a few emails reporting that the popular Embed Artwork script wasn't working in Lion. At first I presumed it was because iTunes wasn't aware that artwork had been downloaded, which the script detects from a track's downloaded property. But it appears that it just doesn't work in Lion.
So, I wrote Re-Embed Artwork, which sort of does the same thing by going the long way around: it exports the image data from a track with artwork as a file and then re-imports it. The image data then appears as the icon for the track's file.
This particular script is a Cocoa-AppleScript applet that can only run in 10.6 and 10.7, but you'll only need to use it in 10.7.