Grant Holliday, who runs the busiest TFS at Microsoft, posted 6 handy reports you can easily import into your TFS to monitor system performance.
"We have a responsibility to ensure that the server is performing as expected and to identify any efficiencies that can be made in the server or the tools. To do this, we have created a number of reports that we use ourselves and make available to our own users."
Link: Read the full story and download the Report Pack.

Far too often people install Visual Studio SP1 before Team Explorer 2008 and therefore TE remains unpatched in the RTM state.
Luckily the ambitious TFS Admin can use the TFS Server Manager from the Power Tools package (TfsServerManager.exe in the Power Tools folder) to find those users without SP1:
Check for VS 2008 SP1 from the server
Open "Completed Requests" in TFS server manager.
Choose "devenv.exe, 9.0.21022.8" (= RTM), devenv.exe, 9.0.30729.1 stands for SP1.
Click "Run Query" and look at the User and Client IP columns to identity your colleagues:
Done!
Visual Studio (devenv.exe) Version Numbers:
- devenv.exe 9.0.30729.1 – Visual Studio 2008 SP1
- devenv.exe 9.0.21022.8 – Visual Studio 2008
- devenv.exe 8.0.50727.762 – Visual Studio 2005 SP1 (?)
- devenv.exe 8.0.?? – Visual Studio 2005