Sometimes you are in ViewModel X and you want to execute a command on ViewModel Y. You do not want to link the 2 because of some constrains that that might impose. How can you leverage MEFs capabilities to overcome such a situation?
Easy have the ViewModel Y expose the command as a property just like you would have it for binding from the View, but also add an Export attribute on the property and give it a name
Now from ViewModel X simple imports the ICommand by specifying that same name (yes you can have the string as a constant, also I would advice to use constants to avoid conflicts in strings)
MEF will automatically get the command from ViewModel Y into ViewModel X for you. This works very nicely with MEFedMVVM since MEFedMVVM resolves all ViewModels via MEF thus you do not need to do anything to resolve the ViewModel or anything. You simply decorate the properties for Export and Import and viola you can start drinking beer