>The MSN Messenger Activie API is one great example of something working today, see http://msdn.microsoft.com/library/default.asp?url=/library/en-us/messengerp2p/overview.asp.
>
>That is a very pleasant interface.

The Activity API object model is documented at http://msdn.microsoft.com/library/default.asp?url=/library/en-us/messengerp2p/techref/objectmodel/index.asp. Now imagine more online services like this, for http://www.live.com/ and technologies from http://labs.live.com.