If you haven’t already heard, the Release Candidate for 1.0 of ASP.NET AJAX went out yesterday evening. We already migrated to it here and it’s quite painless. You just need to reference the new assemblies which have been renamed to from Microsoft.Web* to System.Web*, changing a couple of namespaces and patching up your web.config. All the details of migration from Beta2->RC1 are documented here. These late breaking changes were made in anticipation of merging with the .NET framework in the Orcas timeframe.
So, what are you waiting for? Go download it!