It might matter to some extent, somwhere I was reading up on diffrent stunts/techniques and they said that the foot you keep forward should be a certain one based on wich is your strong leg and wich way you lean when you do a track stand for optimal balance. I have no clue what link I was looking at tho.
I have a bad habit of left foot down as a road rider, but when I start going offroad im sure thats somthing I will correct quickly or pay the price for it by falling.