Thanks to Eric Schoonover
and Mike Ammerlaan
, we now have UpdatePanel working in SharePoint. To get UpdatePanel in your web part you can derive from Eric's AjaxBasePart (Note: In this sample Microsoft.SharePoint.WebPartPages.WebPart v2 is being used rather than the System.Web.UI.WebControls.WebParts.WebPart v3 so you need .dwp instead of .webpart definitions if you are deploying your web part as a feature). For RAD development, head over to Jan Tielens' Blog
for his SmartPart with AJAX support. It's great to see many people have caught the Ajax in SharePoint bandwagon, hopefully we'll see more flashy enterprise applications developed for MOSS/WSSv3 soon!