https://github.com/teradeep/demo-apps/tree/master/generic-em...
or this:
http://mxnet.readthedocs.org/en/latest/tutorial/smart_device...
Not really RPi related - but I think it's only a matter of time until we have mobile GPU optimised BLAS libraries working with Mali, Adreno etc. At that point machine learning will become more feasible on current mobile devices