Stack agnosticism: how and when to swap in stack substitutes?
One of the central ideas to the Rails 3 version is that each part of the standard Rails stack is replaceable. Use practical examples of swapping in substitutes and, even, how to write your own substitutes and properly hook in.
I’m thinking of covering how to swap out ActiveRecord with something else, like Datamapper or Mongo, or both. Do you think this would be worthwhile?