I'm not a contributor to this project, but I have several customers who use the Test Edition of VSTS because it's an easier way of testing new frameworks than the other alternatives.
I case you haven't seen it, here's the project description:
This tool takes a WCF trace file and a WCF client proxy, or a WCF interface contract, and generates a unit test that replays the same sequence of calls found in the trace file. The code generated is easily modifiable so that data variation can be introduced for the purpose of doing performance testing.
The tool generates code for both Visual Studio 2005 and Visual Studio 2008. It also installs a wizard into both editions of Visual Studio for creating the trace and processing it from inside Visual Studio. If both editions are present the tool is installed into both editions. The source code is a Visual Studio 2005 project.
The features are listed out on the project site (WCF Load Test - Home), and it's been in use for about a year before it was published out to CodePlex, so I'd feel pretty safe with it. It was put together by members of the "VSTS Ranger Team", who published the TFS--Project Server 2007 Synchronizer and the VSTS Guidance on CodePlex. Bijan Javidi and Rob Jarrett published the code, and apparently Rob was the key writer of the code. Bijan is one of the key rangers at Microsoft.
Since it generates a unit test, it's really easy to modify it, or inject it into a load test.