It'd be cool to focus on a conversation in Mail.app and be able to add all of it to SFDC via maildrop. Maildrop would intelligently only upload those messages (both sent and received) which have not yet been uploaded.
New contacts often mean new accounts. It would be cool if they could be created together instead of having to backfill that information on the web site. Also, showing a list of existing accounts to pick from would also be cool.
When adding an email, maildrop (excellently) searches for the contact with the email address of the sender. It would be cool if it also auto-populated the "Related to what?" list with opportunities related to the sender.