I saw pretty great results switching a pretty “standard” high traffic Python web app (Flask & uwsgi) over to run on PyPy. We saw about 30% faster response time for HTTP requests, several times the number of tasks/second on the workers, and we were able to scale down the total instances needed. Mostly the typical Python web app libraries just worked, and I spent a couple of days making sure everything was stable, but it was a great success overall.