Yes, though only on a single app -- a reasonably high-traffic content site. In this case, PyPy is roughly 10% faster (measured by comparing total view rendering time) but consumes about 2-3x as much RAM.

Edit: I should clarify: this site doesn't use a DB engine but instead is pulling and rending content from an XML DB over a REST API. See Alex's note below about DB performance for why this is an important point.