Some requests for the JavascriptSerializer: 

• I'd like to have a way be able to put javascript literals in my JSON output, like an element id or an object reference.
• The ability for a custom converter to return a scalar value instead of a dictionary (just change the return type to object)
• attributes to set output property names like the XmlElement attribute for xml serialization, my casing in javascript is different than my casing in .Net server side code so I either have to do a custom dictionary to sync names or just break naming conventions on one side or the other

Thats the majority of issues I've run in to so far, they are actually very minor issues and should be no problem to address.  I have actually done them locally in my own JavascriptSerializer I decompiled from the Ajax one and each one only resulted in a few lines of code.