ASP.NET AJAX 1.0 has RTM’d, so go get it and get started creating a better web experience for your users. Also be sure to check out the toolkit which has a bunch of common controls that you may find useful.
We (Mimeo) are going to be releasing a couple updated features to our application this weekend that are built using ASP.NET AJAX. In the March timeframe we will have released our first phase of migration to using ScriptManager for all our script management (instead of ClientScriptManager) as well as upgrading a few more of the site features to use UpdatePanels. In the next phase we will overhaul all our existing scripts/server controls to use the ASP.NET AJAX class/control model instead of a proprietary one we’ve been using.
Kudos to the team for getting this baby out the door! I’m looking forward to the “Orcas” timeframe when this is no longer an add-on to the System.Web framework and we actually have better development support inside of Visual Studio.