On the Golf Channel they mentioned that when the PGA was at Whistling Straights in 2004 (I think), Stuart Appleby was penalized 4 strokes for doing the same thing that Dustin Johnson did. The difference was that in the previous tournament, there were sand bunkers and waste bunkers on the course. Appleby thought he was in a waste bunker, where you can ground your club, take a practice swing, etc. It was deemed he was not and he was penalized. A rule was put into place for the 2010 PGA that all bunkers would be considered sand traps and there would be no waste bunkers. That being said, even a waste bunker would not generally have fans wandering around in it. If you watched the final hole and the tournment, you noticed that it was said several times that even the club doesn't know the number of bunkers on the course, it is estimated to be 1200 but new one appear and old ones disappear from time to time. How can the players know what is and isn't a bunker if the club doesn't really know. The area that Dustin was in looked to me to be a worn area, remember the course is lake side, that has some sand showing due to the crowd standing there. Just before Dustin hit his shot, I noticed a PGA rules official just to his right standing in the bunker, I don't believe he knew it was a bunker. While it is up to the player to ask the rule official about something he is unsure of, in this case I think the official would have told him this was a bunker if he thought it was. The PGA got this one wrong and denied a good young player a chance of his first major win.