Configuring Active Directory Web Proxy Client Autodetection
Forefront TMG uses Active Directory (AD) Marker for automatic detection of the location of Forefront TMG. The TmgAdConfig tool is an autodiscovery tool which configures Active Directory with a marker key that points to the Forefront TMG computer. This key is used by the Forefront TMG Client to locate and connect to the Forefront TMG computer.
This is a really great feature that I don't see used enough - learn more about it over at: