From Karl Seguin: Learn how AJAX (Asynchronous JavaScript And XML) can be used to make your Microsoft ASP.NET applications more dynamic and responsive:
Introduction Since the start of Web programming, numerous tradeoffs have existed between Web applications and desktop applications. For example, it has been generally accepted that Web applications don't provide the same type of rich user interface as desktop applications. On the flip side, Web applications are platform independent and provide an easier development mechanism. One area that's been a continuous battleground for Web developers has been the seemingly simple task of providing more responsive applications.
Read full article on MSDN: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/ASPNetSpicedAjax.asp [1]