When communicating in a .NET to .NET messaging scenario then optimizing the data contracts is an additional way to reduce the SOAP message size. This together with binary encoding will reduce the message size about 4 times. Especially looking to the Windows Phone 7 development this will help much when the traffic goes over a low bandwidth network like GSM or UMTS.
From our Silverlight application we must be able to view documents. Documents are stored in an existing document management system and are accessible through a WCF REST service. It sounds very easy, but it was quite hard to understand all the stuff going on behind the Internet Explorer and the Microsoft Office.