This is how I feel about Flask.
I've been using it with Backbone.js and they make a great combo: Flask API serving JSON, and the rest of the logic on the client.
Is there any of this solution that bundles with an easy mobile library/sdk? I was asking for something like a semicomplete backend opensource solution here http://news.ycombinator.com/item?id=3735387 but unfortunately I got no responses
I believe Twitter and Foursquare are doing this too. Their Scala-based appservers are API endpoints, serving JSON to the javascript/Backbone.js frontend.