MEFGrid is a sample MEF application that I presented at Seattle Code Camp and at an Olympia .NET user group meeting. It includes connect 4 and the game of life, but other grid based games could be written and dropped into the extensions directory.
The application demonstrates some of the more advanced features of MEF. The available life patterns, for example, are stored as text files in the LifePatterns directory. A custom catalog makes these available as string-based exports via a custom programming model, and the life game uses a contract adapter to convert the string-based exports to command exports that set the current life pattern.
If I can find the time I will write a series of blog posts explaining how the application works in more detail. For now, feel free to post questions in the comments or on the MEF discussion forums.