OTOH did you know TwentyTen displays thumbnails as replacement headers and not in the body of the post, a decision I challenged unsuccessfully. If the thumbnail isn’t the same size as the header, it won’t show anything at all! I still can’t fathom why anyone thought that made sense.
II have some code to display a thumbnail in a Trac ticket but I can’t access it right now since I’m typing on my iPad and afraid I’ll lost this if I switch tasks and go looking for it. Just look for a thumbnail-related ticket under my name.