I still use Scala though for data / computation intensive code. The setup is REST API with Flask, add to queue to be dequeue by the Scala worker. I really like the combination.
Will use in the near future: Flask and/or Node.js
You don't use any additional framework? Does this mean you manually have to code POST requests to accept data / save them to the database? Some kind of REST framework would seem like a far easier option. (I use Django / Tasypie - you configure the resource, and it automatically knows how to save a valid POST to the database).
In general, the whole point of using microframework like flask is to keep a tight control of your code base. You may think that some low level libs would be too hard to code, and you would be right, but most of time you can avoid the difficulties by coding only for your specific case.