Well that's cool, I didn't even know that. In my defense, I read the documentation which doesn't say that at all:
It reads...
"Return Value
truetrue (True in Visual Basic) if all of the commands return truetrue (True in Visual Basic); otherwise, falsefalse (False in Visual Basic)."
This is exactly what I need though, I have a Export menu command which each view/viewmodel implements differently. I only want the active one to be executed. My views and viewmodels are already IActiveAware so all I need to do is toggle the IsActive of the corresponding DelegateCommands it sounds like and add them to a composite command.. I'll give it a try!