A few days ago, I wanted to send a quick thank you to a friend. I opened up a new Firefox tab, clicked my email shortcut link, logged in, clicked compose, typed my friend's email address, entered "thank you" as the subject, a very brief thank you message in the body, and clicked "Send".
What I really wanted to do was type the following in my YubNub command field:
rss jsmith2005 hey thx for the tip! -sean
rss (a not-yet-created YubNub command) communicates with an RSS message server (not yet created, as far as I know) and posts my short message to my friend's personal RSS message feed. This example uses YubNub (because it's so sweet and simple to integrate with an exposed API) but other standard methods would work too (web app, desktop app, wireless app, etc.)
John Smith could set up his personal message feed to accept anonymous messages like the one above (my name is simply part of the message text, not a true identifier,) or could require some form of sender authentication. This would be done on the sender/server side. Jane Smith would choose a feed name which she could make public or tell only to her friends and associates.
Personal RSS feeds might be easy to abuse. A bot could flood a public message feed with spam quite easily. If John Smith so chooses, he could require a form of password to send him RSS messages:
rss jsmith2005:kyoto hey thx for the tip! -sean
If the password is missing, the message would be dropped or forwarded to Jane Smith's spam message feed.
Why waste an email on "hey thx for the tip!" I certainly don't want to.