Here's a useful site that provide a way for you to create an animated indicator progress icon that you can easily use with the AJAX UpdateProgress control to visually indicate a callback operation.
http://www.ajaxload.info/
This service pack includes full support for SQL Server 2008 (including support for new date and file stream capabilities), new features for ASP.NET AJAX, performance improvement for WPF, and more!
http://www.microsoft.com/downloads/details.aspx?FamilyId=AB99342F-5D1A-413D-8319-81DA479AB0D7&displaylang=en
After implementing the AJAX Extension from ASP.NET 3.5 in my family portal website that we use to organize our household, I've gained much more confidence with UpdatePanel controls. I still need to make some minor tweaks to it; but for the most part, I love being able to produce a web application without all that page refreshing.
However, I also know that I have more to learn about AJAX, and that there are more features that I can take advantage of. A cool way to do that would be to use controls that have AJAX built-in. In my ASP.NET 1.1 and 2.0 days, I was introduced to Anthem.NET, which gives you controls that encapsulate the complicated code needed to make AJAX work. Therefore, we were able to simply replace regular ASP.NET web controls with Anthem controls that responded to callbacks instead of the normal postbacks.
There is also an open source project developed by DotNetSlackers called the AJAX Data Controls (ADC), which is developed on top of the ASP.NET AJAX Extension. My man Jason Gaylord has been using them for a while, and has just recently joined that development team to convert these controls for ASP.NET 3.5 and Visual Studio 2008. This set of controls are now available for download, which includes a GridView, Repeater, DataList, and Page controls.
I'm hopeful that I'll gain more AJAX functionality out of the box with these controls than I could implement on my own, along making my AJAX development more efficient. Of course, I'll keep you posted either way; but if they're good enough for Jason, I'm confident they will serve me well.