Script Callbacks in ASP.NET

I am sure that every web developers hates page refresh. And everyone chases the way to make its page more interactive without postback. The best way is client side scripting, but it is not enough to generate all page activity. Javascript based technologies like callbacks and AJAX are at the bottom of the effcicient developer's code.
Here are some good posts for callback technology in ASP.NET 2.0.

http://msdn.microsoft.com/msdnmag/issues/04/08/cuttingedge/

http://www.developer.com/net/asp/article.php/3485991

http://www.mredkj.com/vbnet/scriptCallback.html

At the core, ASP.NET script callbacks consist of some client-side JavaScript code needed for asynchronous communication to the server. The first requirement for using the callbacks is that some server-side code awaits client calls. The client-side callback intermediary manages the call while the user continues to see the old page and interact with it.