Using the beta version of Visual Studio 2010, and trying to connect to a Team Foundation Server, you may find that you get the error message:
"The ServicePointManager does not support proxies with the https scheme."
You'll only get this of course if you are trying to connect using HTTPS / port 443. The workaround seems to be some reg fixes which tell the TFS client to bypass the proxy.
Aaron Block's MSDN blog seems to have the answer to this: