I have been working on a couple ASP.NET applications. I have been using AJAX.NET with the applications. AJAX.Net offers an easy way to include ajax into you web pages.
One thing Dan and I came across as we were using the UpdatePanel of the AJAX.NET framework was for some reason it would not work with with RadioButtonList (RBL) control. We had no problems getting async post backs to work on control changes of DropDownList, CheckBox, and Button controls, but for some reason the RBL control doesn't quite work right.
I could go on to explain why but I think this post does the best job of describing the problem and the solution.... http://smarx.com/posts/the-case-of-the-radiobuttonlist-half-trigger.aspx
Other than that problem the AJAX framework has worked well.