Why json

there's a new generation of client-side JavaScript frameworks - http://backbonejs.org/ is what I'm most familiar with. The client side interface has become so rich that it now needs a proper ORM.

This is _not_ to say we do away with all the sever-side infrastructure you mention (though a few sites seem to go most of the way) - in general there seems to be a hybrid approach where a subset of date is mapped client side for manipulation by the rich interface there.

Of course you want to avoid duplication of models between client and server-side, and of course you still need to validate data - the trend is to reduce the server-side representation, not eliminate it completely.