Not for 'proper' production (still missing a few libraries and C++/swig related stuff), but I have a collection of scripts that I use all the time that reads in data from various sources, does stuff to that data and then writes out that data to new files. Typing "pypy foo.py" instead of "python foo.py" gives me a 3-7 times speed up without having to make any changes to the source code. Can't really argue with that.