I've been meaning to comment on the Celtic's lack of boxing out for a little while now, so great topic. There was a play in particular where Wade got his own rebound about 10 ft from the hoop simply b/c Ray Allen put 0 effort into boxing him out, and it really frustrated me. Ray is not alone either.
I disagree that in the NBA rebounding is mostly athleticism. It certainly matters more than a pickup game, but boxing out / positioning is still the #1 fundamental of getting a rebound. A player intuition also seems to count for a good deal, but intuition doesn't do much good to a player if they are effectively boxed out.
BBD is doing a great job on the O-board, but his boxing out on the defensive end is typically too far under the hoop (and thus his height limits him). Pierce used to box out more, but still does a good job. Perkins does a great job, and so does KG. Rasheed is pretty good. Ray does a terrible job. Rondo's rebounding is from a position that rarely utilizes boxing out. Scalabrine is usually too far from the hoop, and so someone athletic can get around him. He's also too slow to turn and effectively box out. All in all the team really needs to get back to boxing out consistently, and take care of the ball!