We'll offer binary serialization (aka "Binary message encoding") in the next version of our "DevForce for Silverlight" product. We're quickly incorporating Silverlight 3 features and this is an important one. We had to rely on text encoding heretofore because that's the best that Silverlight 2 could offer.
Read this to learn why binary serialization matters. According to Microsoft, we should be seeing smaller payloads and better service performance. This March 9th bulletin promises "a follow-up post ... with some specific data on the improvements that can be expected"; haven't seen such follow-up yet and we haven't measured the difference ourselves ... yet. It sure makes sense in theory. More on this subject when there is more to say.