A couple years back, many RSS clients started communicating subscriber data to FeedBurner via the User-Agent HTTP header. Now Fedafi wants to do the same thing. I think it's time that the RSS Advisory Board formalize some of these mechanisms. I'm going to include this in my RSS Feed State document and recommend it for adoption by the board.
http://blog.fedafi.com/2007/01/12/rss-subscriber-standard-for-user-agents/
Marcel
Randy
Rogers Cadenhead