Like Ayende said, It walks like a duck and it talks like a duck but it’s still to be determined what it wants to be. MEF looks like an IoC container but is it really that? No not really. Anyway here are some very good examples of what you can do with it.

The Microsoft Extensibility Framework

Simple Introduction to Extensible Applications with the Managed Extensions Framework by Brad Abrams

So I added brad to my ever growing list of blogs to read. One wonders when I actually find the time to get some real work done.

About the difference between MEF and System.Addins by Krzysztof Cwalina

And this is what they have to say about their own framework.

The Managed Extensibility Framework (MEF) is a new library in .NET that enables greater reuse of applications and components. Using MEF, .NET applications can make the shift from being statically compiled to dynamically composed. If you are building extensible applications, extensible frameworks and application extensions, then MEF is for you.

Disclaimer: MEF is in development. The source available on this site, does not reflect the final state of the product. It is also not a CTP, Beta or anything similar. It is very likely that the APIs within will evolve and change. If you are downloading the source, consider it a preview of where we are at currently. We welcome any feedback you have on your experience.