I did my first project with AJAX.NET a few weeks back. I had done things with AJAX before (as in, before it got that candy-a** name) and I like the idea, but AJAX.NET pretty much cut this project down from a 3 week investment of my time to 2 days. It also saved me from having to write XSLs, which is awesome.
It cut all of the grunt-work out of using AJAX and made utilizing it a nice, clean experience. I rolled it out to my site and no users have reported browser compatibility issues (and my users are, by and large, well ... users ... as in their microwaves are still flashing 12:00). AJAX.NET is definitely the future for my sites.
Edit: http://700level.com/fansview/memberlist.aspx is the location of the page. Do a view source and check out the javascript at the bottom of the page. It's not complicated, but I spent nearly the entire time writing that instead of writing an AJAX engine. The server-side stuff is just 1 method that returns a dataset that's sorted, filtered, and paged (which might be worth an entry of its own later).