Tnis plugin is so useful it is a MUST if you oon"t want to have an unmanageable media library in no time.
One suggestion though, I would love to be able to repalce one image version only (say the medium size). Sometimes, the client wants this one to be cropped and show differently and it is very important for marketing purpose. So I have to work on it and reupload by FTP, that is something they certainly would not do on their own. WOuld be great if they could do through WP admin with this plugin?