I added the HTTP header value ETag [1] to my scripts that they can be cached on the client. This will fasten up initial loading of the complete page if the scripts are not changed, what is the default on running systems. I think this feature was missing in the old library, all the client-side stuff was sent to the client.
Do you want to see what Ajax.NET Professional is sending from and to the server? Use the Fiddler HTTP Debugger [2], one of my favorite tools developing web sites.