I hope in the RTM you'll get more help solving your WCF Ajax problems then I currently get, because I'm getting mad from time to time. In my quest for getting things to work, I learned some stuff I wanted to share. Read: have a checklist for myself because I tend to forget this kind of stuff! ;-)
<%@ ServiceHost Language="C#" Debug="true" Service="WebApplication1.WCFAjaxService" CodeBehind="Service.svc.cs" Factory="System.ServiceModel.Activation.WebScriptServiceHostFactory"%>
When I come across more I will post them here, including an update comment.