I grew up watching old kung fu movies where they crack open walnuts by squeezing their hands. It's always been a dream to do that, but I've only done it like that 2 or 3 times. I stopped using my hands for nuts in general after a pistachio seperated my thumbnail from my finger. x_X
I usually just pop a knife in and twist for walnuts.
Well, I like big black walnuts, which take a lot of handling. I have to put my nuts in one of these babies:
Works great, as I've never failed to bust a nut with this. The downside to using it is that the pressure really builds up right before hand, and all the nut goodness goes flying everywhere if you're not careful.