I've just found a solution to a problem I was having.  Using SL2 when adding a service reference to my WCF service, my project compiles fine, but does not run.  I get the error:

"Unrecognized element '' in service reference configuration. Note that only a subset of the Windows Communication Foundation configuration functionality is available in Silverlight."

It turns out this is only a problem on Windows 7 rc. In your client side service reference file, something like MyServiceReference.ClientConfig, you'll have:

The fix is to remove the <security> element above that is circled.  Apparently this is not valid and only happens on Windows 7 RC.