This is a great way to put a face to people I correspond with. Very easy to set up, and automatic in use. Best of all, emails that I send <i>aren't</i> unnecessarily long; if the recipient doesn't have this capability, then they'll never know the difference.
Two small problems: there seems to be some conflict with GPGMail, and MailPictures can't get images from servers that use a redirect URL due to limitations in Apple's code.