Dustin Metzgar recently posted an entry centered around understanding how ASP .NET and WCF work in order to avoid unnecessarily blocking threads.  He used a couple of different tools to examine the problem, including the Concurrency Visualizer.  See his entry here: http://blogs.msdn.com/b/dmetzgar/archive/2011/06/14/request-threading-in-asp-net-and-wcf.aspx

James Rapp – Parallel Computing Platform