Walk into a room, any room at all, anywhere in the world. Look around that room, then announce, at the top of your voice:
Everyone, please hold up your sharpy.
Look around. Everyone in the room that holds up a sharpy is a magician.
Haha! Very true. BUT, You wouldn't do that would you, you'd walk into a room and ask to borrow a pen. Even if you asked to borrow a pen or a pencil, chances are you're more likely to be handed a pen.
Still, as Seige points out, it's horses for courses. Fair point on the bleed through and I guess if you don't draw attention to the fact that you're using a pencil no one will question it.