If I download something from someone I'd like them automatically added to my user list. Perhaps in a group named "Downloaded from".<!--break-->
If someone downloads from me perhaps add them to a group named "Downloaded from me".
If we got fancy, I'd add to their Notes a what was downloaded in summary (filename if a single file, folder name if a whole folder say). And maybe two stats, the total data volume I've downloaded from them, and the total they'd downloaded from me. Just so I can keep a track of where good Karma is playing out ;-).