I just found out that the RTM bits are available for download:
ASP.NET AJAX Extensions
ASP.NET AJAX Futures CTP January
ASP.NET AJAX Control Toolkit
Update: Scott Guthrie also wrote a, more lengthy, article about it on his blog. Apparently they're also releasing the source code of the Extensions (UpdatePanel, UpdateProgress, ...). Personally I think this is great news and could help in the adoption of this AJAX framework.