The way I understand it, The new Async-Await functionality in the C# 5 CTP should be all implemented in the compiler. This should mean that code compiled with the CTP should be able to run on vanilla .Net 4?
Can it?
The Async CTP was replaced by the Async Targeting Pack for Visual Studio 11, available via Nuget.
This is official, supported, and allows redistribution.
With this library you can build async applications that target (vanilla) .NET 4.
You should also know that you can target .NET 3.5 with the help of AsyncBridge for .NET 3.5 - a small library put together by Daniel Grunwald, Alex Davies and me.