A couple of people have contacted me in the past wanting more details on how to subscribe to the various events that we expose in TFS. Currently our documentation/SDK probably isn't as detailed as it will ultimately reach in this respect.
However, Howard Van Rooijen (of Conchango's Scrum For Team System fame) has managed to put together a template project which creates SOAP endpoints for our core notifications and even performs basic deserialization.
Here's the link. Team Foundation Server Notification Web Services: Visual Studio 2005 Project Template
This is very cool - I'm sure it will be extremely useful.