I do it. I think it sort of gives me a sense of comfort. But it seems to run in the family - on my father's side. My dad shakes his leg. As do my brother and yours truly. My paternal grandfather is a leg-shaking champion. I can't say for sure, as he is dead, but I'm pretty sure my paternal grandfather's father would out-leg-shake us all combined.

And then, on my mother's side, nobody I can think of does it. My mother hates leg-shaking. I try to be decent about it when she's in the room. Fortunately, my wife - who doesn't approve of legshaking, and seldom shakes a leg - doesn't really give me grief about it. Guess she's written me off as a leg-shaker, and accepted it as one of "those" things.