I have the feeling that if you look for the best effects of agile, it will be found in projects that involve a limited number of users who want to do a specific thing in a non-agile environment.
and this is where the case studies are performed (funny that).
limitations of agile will be found when _every_thing_is_agile_ .
so every project is continually redefining its interfaces / scope.
In a big organisation, that might not work. In a small organisation, it might - in both cases it will be extra effort from the users (one externality) that really makes it work.