Simone [1] has finished the survey and published the results of the survey about the usage of AJAX among .NET web developers [2]. The results are very interesting. The most used AJAX toolkit is ASP.NET AJAX [3] with about 73.7% followed by the AJAX Control Toolkit [4] which is used by almost half of the .NET developers that are using AJAX.
The second mosed used framework after the Microsoft one are my Ajax.NET Professional [5] and jQuery [6], both used by 13.3% of the users. As I know there are many web developers that are combining jQuery and my lib because they fit together very good.
I'm very happy to see my library right after the Microsoft ones. As this is a private project only I see that the idea of use AJAX only for data exchange is still alive. I still prefer the use of AJAX as a REST interface, doesn't matter if it is a web application written with HTML/JavaScript or Silverlight. I love the JSON [8] format! The feedback I get from other web developers often is that they try to use a third-party control, working with it, stumble over several errors or behaviors they cannot live with, and then creating their own controls using an AJAX framework/raw XHR combined with a great JavaScript library like jQuery.
For more details have a look at the full story: Simone's .NET AJAX survey results [2].