The Team Foundation Server Power Tools (October 2008) introduced a new "Team Members" node, which offers the ability to quickly identify which subteams and actual team members belong to a TFS team project. Additionally you can see their online status.
Support for Office Live Communicator and Windows Live Messenger is already built-in. There is an API to extend this to other IM software as well.
Nico Orschel from our team used this API to implement support for Skype, which is the IM we primarily use at AIT TeamSystemPro Team.
Our Skype Collaboration Provider (including source code) can be found on Codeplex at: