ASP.NET Ajax Library provides some client-side events. For instance:

Sys.Application.add_load(
    function(args) {
        // handle the end of any asynchronous post-back. Every-time there's
        // a server round-trip, this method will be called.
    }
);

During the asynchronous post-back I want to retrieve information to the client. This information must be available in some event like the discribed above.

Does the UpdatePanel or the ScriptManager have any server-side way to retrieve data back to client during an asynchronous post-back?