Apps on OS X that have been installed through the App Store are sandboxed which is pretty close to the partitioning on iOS - for instance they can only access files the user has explicitly given access to (open dialog, double-clicking, drag and drop onto the app).
That doesn't help you with apps you downloaded through the web though, which for me is all my apps because the App Store is a PITA.
That doesn't help you with apps you downloaded through the web though, which for me is all my apps because the App Store is a PITA.