What is a GeoChat Layer?
A geochat layer can be created by any ArcMap user. The layer creator can add one or more MSN contacts to the layer. When the layer creator sends a text/geometry/imagery message to the layer all recipients (that are running ArcMap + geochat) will be “pushed” the layer and the associated message. All contacts are then free to send messages. Note that all geochat communication is peer to peer (P2P). One nice feature of geochat layers is that they can be used in the geoprocessing environment!
GoeChat was mentioned a little bit at the ESRI User Conference, but unfortunately I was never really able to find anything more in detail. Well Richie has a great post about how the product works as well as some nice screen shots of it in action.