Just wanted to mention that JavaScriptSerializer, which was marked as obsolete in .Net 3.5, seems to be restored back to normal status with SP1. Besides checking in the object browser, the only confirmation I found for this was a comment by Scott Gu on this blog post.
This is good news since JavaScriptSerializer does seem simpler to use and can handle anonymous types as well. Its alternative DataContractJsonSerializer is meant more for use with WCF.