I've just been checking out the progress of pypy (specifically whether or not pi3d will 'just' work with it now) On ubuntu it was surprisingly straightforward and worked very well, just four numpy functions missing (that had little impact).
On the Raspberry Pi, although pypy is already installed on raspbian jessie, the pypy version numpy needs a later version (v4.4 c.f. v4.0). But there is a binary available for raspbian (v5.7.1) and instructions on the pypy docs. However some things were a little obscure so I have written up the steps I took in the pi3d FAQ section. Hopefully someone will find this useful at some stage.