Microsoft seems to be about reinventing the wheel again, Krzysztof blogged about a new framework being worked on with these goals:
MEF is a set of features referred in the academic community and in the industry as a Naming and Activation Service (returns an object given a “name”), Dependency Injection (DI) framework, and a Structural Type System (duck typing)
They are currently just experimenting with different approaches and a CTP is likely to be released soon. The example that Krzysztof showed might not be indicative of how it will eventually turn out but it doesn't look very promising (requiring property attributes to declare dependencies, etc).
The approach I was hoping that Microsoft would take was to try and incorporate the concepts of an IoC container but make the concrete container pluggable. Maybe even to introduce this concept on the CLR level or maybe just C#/VB. Maybe something like this:
this.authService = resolve IAuthentificationService
If C# could introduce a new keyword (resolve) that would request a component from a container. The .NET framework would probably need a basic implementation of the container but it should be completely pluggable so you can exchange it with for example Castle Windsor or StructureMap. I haven't really thought this through but If Microsoft is going to include an IoC Container in the core framework this is the approach I wish they would at least try (maybe they have?).