That said, there is something tidy about the idea of writing web applications in two intertwined but separate tasks:
Writing JSON web services and separately unit testing them
Interactively developing the client side with a framework like Mjt
I like to recognize technologies as early as possible that I might use in the future. Although I don't (yet) feel really comfortable working with frameworks like Mjt my gut feeling is that this is the future because it makes it easier to work with multiple languages and platforms for implementing web services and makes it easier to mix up data from multiple sources.