I just stumbled across a wonderful "publish/subscribe" application at Folgers coffee's site TolerateMornings.com. It is a "BossTracker" that allows office workers to build a customized map of their office and then have people update the application with sightings of the boss as he/she wanders about the office. Of course, everyone is then notified of the boss' current location in graphical detail. There is more to publish/subscribe than blog posts and SEC Edgar updates... The basic pattern of publish/subscribe has endless applications.
Similarly "odd" applications of publish/subscribe are the services that MySpace.com has recently started shutting down with Cease and Desist letters... Until recently singlestat.us and DatingAnyone.com would let you "subscribe" to the "relationship" status of people on MySpace. Thus, you could find someone you really wanted to date or otherwise pursue, but if they were "currently in a relationship" you could ask for an email to be sent as soon as their status changed to "single." Just another Pub/Sub application. Tell the system what you're interested in and you'll get a message when it happens.