A new feature in Silverlight 4 is the ability to consume REST/POX (XML) services in a strongly-typed way, using the same programming model as the desktop framework. That includes WebGet/WebInvoke attributes, UriTemplates and body styles. By default, only XML is enabled, but there are extensibility points which can be used to enable the consumption of JSON and Raw services as well (i.e., the full web programming model of the desktop framework).
I posted about the out-of-the-box support for consuming REST/POX services, and I also added another post about using the extensibility points to consume REST/JSON services on SL4. Please let us know what you think!
Silverlight WCF Team