Jabber in Radio
I think it's only fair to mention that there is something VERY innovative happening in User-Radio-land... Jabber connectivity (note: link points to a Radio/Frontier ODB file). Jeremy Bowers and DJ Adams appear to be heading this effort, with strong cooperation on the part of UserLand.
Jabber is freaking cool(tm), and being able to use that network for prescence and event notifications, message routing, etc. is going to be wild. Especially once people build real apps on top of that plumbing. In the mean time it'll be a hell of a playroom for geeks!