The Service Bus and Access Control online services through Windows Azure AppFabric have now moved from being a trial service to a fully supported service. The service bus is an infrastructure piece for connecting together different components in a distributed application. The access control service allows you to integrate those connected components with a variety of identity providers. Both of these services can then be used together with the application services that you develop for Azure.
The official start of Azure AppFabric services also comes with an updated SDK release. The main download for the April 2010 SDK includes the SDK libraries, documentation, and samples. Consult the release notes for a description of the breaking changes and known issues in the release.