Flex.NET
I thought this would be of interest to you. We just launched a public beta of the 2.1 version of our product - WebORB, the new release is a full implementation of Flex Data Services for .NET. We have added AMF3 support and now anyone using Flex on the client-side can integrate it with the .NET backend. Currently we fully support the RPC services functionality from FDS and are working on adding Messaging and DataService. Essentially, WebORB will become a .NET implementation of FDS, and anyone using Flex Builder can continue to develop the client side there.
There are a few articles describing the integration: First is an overview of creating a Flex application and wiring it up with the .NET side. You can access the article here: http://www.themidnightcoders.com/articles/flextodotnet.htm
The other article describes a new feature we added for Flex clients. The feature enables developers to fetch any type of object from the server, modify its contents and then automatically sync the changes from the Flex application into the original object instance on the server-side. The feature is called object auto-update. There is a live example, client and server-side code in the article: http://www.themidnightcoders.com/articles/objectautoupdate.htm