This is a slightly belated post, but recently I gave a presentation to 60+ rails developers in San Francisco about the evolution of the Rails application, and how it all fits together. Presentation, dramatically named "Rails in the Real World" is available on SlideShare. EDIT: I've updated this presentation for MagmaRails conference in June 2012 (presented in Manzanillo, MX), and the updated presentation is the one that should be viewed. Please see this post for the actual slides.
Tech ramblings by Konstantin Gredeskoul