If you are going to start using TFS 2010 please be aware that each TPC (Team Project Collection) needs a separate Build Controller.
For those who are intended to use TFS 2010 as their ALM engine, TFS 2010 can contain several TPCs. Each TPC can contain several Team Projects. Each Team Project is a regular space in TFS that contains Work Item Management, Source Control and Build automation. Build automation in each Team Project contains several Build Definitions that build project with several conditions. Each Build Definition is assigned to a Build Controller. A Build Controller is a build server that builds project using conditions defined in Build Definitions.
In other hands while defining a new Build Definition you must specify its Build Controller. Unfortunately with TFS 2010 you can not use Build Controller defined for say TPC number one for say TPC number two. Each TPC must have its own Build Controller.
Considering that a Build Controller is really a server, assigning a server to each TPC defined in TFS is not very applicable in most companies and teams. There is an article in MSDN blogs that shows a way to use a single Build Controller in several TPCs. As the article itself emphasis, this hack is not recommended for operational installations. Some people like us have been forced to use a single TPC for all Team projects. This work-around has many disadvantages like interfere of Team Projects, security issues, etc, but at least have solved the problem of need to several servers as Build Controllers.