Previously only available for CRM Online, the CRM Diagnostics tool is now released with CRM 2011 Update Rollup 4 for On Premise installations.

It runs a couple of tests, measuring latency to the datacenter, bandwidth, and performs a few Java script performance tests to measure the CPU/browser performance of the machine.

You can access the tool using the following URL after you install UR4 or later.
http://<serverUrl>/tools/diagnostics/diag.aspx