Is there any documents or white papers on the changes made to the REST services. I've read from other posts that it communicates entirely through JSON now. I'm no where near an expert on communication protocol but something has changed along the line somewhere.
My Silverlight application (API 3.1) is having intermittent trouble with the QueryTask. some posts are suggesting that it can't communicate properly with JSON
Extremely tough to read about stuff like this ahead of time so you don't know you're in trouble until it's too late.