MP3Tag is a great tool and so far I use it mostly to add missing cover images. One thing that would be useful for this, when scrolling through the list of files in the main window, would be to show the cover image on the bottom left when one is present in the directory of the file one points at. I believe right now the cover art is only shown when it is attached to the file itself. A little icon could be used to show if the displayed cover is part of the file or in the directory.
On a similar note, when retrieving and saving a cover image only to a directory, the confirmation message says "Saved tag in 0 of 0 files." which is of course technically correct as no tag was changes but it is still misleading or at least incomplete as the 'save to directory' should be confirmed.
Thanks a lot,