Interesting subject. I see a video where they guy uses a PC and not a Pi. This is Part One. Best to see both parts.
https://www.youtube.com/watch?v=j7opj5-32hw
 
This is interesting, as he said to use the GPU and not the CPU as the GPU is faster in solving some things. I can understand that if they are using higher math functions that the CPU may not have, but the GPU is usually 50% slower than the CPU.
 
What does this have to do with Pi's?
 
Though the R-Pi uses the VideoCore VI CPU (as the BeagleBone Black uses a similar GPU), it is too slow for BitCoin Mining though still usable.
 
But others like the Banana Pi and Orange Pi uses the Mali 400 - a Dual GPU for high end video, This is where BitCoin Mining hits it big.
 
I know a few friends BitCoin Mining with a Raspberry Pi, they are not making that much money with it. But some is better than none. I need to rethink this heavily.