I routinely fail to get speedup on PyPy. In fact I frequently get slowdowns. I imagine it's only fast if your code is slower than it needs to be to begin with.
It works well for tight loops processing much data, or heavy object-orientation (multiple levels of class hierarchies). It probably won't work well for regular Django webapps or scripts. Also, real-world Python numerical/AI code uses numpy/ML libs so there's not much to optimize in Python...