Yah.. those are sweet. we've had target practice of a couple house roofs we built. I framed for a couple years, and in that time, probably nicked myself with nails a thousand times. put one through my foot (not my fault) and a couple through my finer tips sideways.
NOTE: do not hold 2x4 on backside. nails will be driven through into hand.
NOTE: do not hold 2x4 on side, nails hit knots in the wood, and shoot sideways.