Last week the ESRI Prototype Lab published a P2P geocollaboration extension for ArcGIS Desktop called G2G. This capability is now available for ArcGIS Explorer users. The custom task can be downloaded here from ArcScripts (full source code is included).
After the installation wizard is complete, the "Collaborate" task can be added using the Manage Tasks dialog (Tools > Manage Tasks...). Please read the previous post on how to connect to the peer-to-peer mesh.
Collaboration behavior in ArcGIS Explorer is a little different from that in ArcMap. G2G for ArcGIS Explorer currently only supports text chatting and the exchange of results such as addresses, notes and driving directions. Results can be sent to any peer simply by dragging a result from the Results window and dropping it on to peer in the Collaborate task (as shown below). To send a result to ALL peers drop the result on the Users node.
Note, that only text chatting is currently interoperable between ArcMap and ArcGIS Explorer.