I'm a little dubious about the whole concept of sharing a controller between views. Seems like all too often you are going to run into situations like this. Which is not to say controller and view shouldn't be separated! Just that the benefit of that separation is something other than reusability of the controller.

Mmm.

It seemed to make sense to me to have the application share everything, and just output different stuff based on which template (web or REST) that it was using. But you raise a very good point -- now I'll (presumably) have to change the behaviour of the application based on which mode I'm in, and that's something I was trying to handle completely using templates.