Most serious one was the diver who spent the entire first dive of the trip (after the check-out dive) playing with his new camera. As he tried to pull the last breath from his tank, the DM saw him with his wide, panicked eyes and gave the diver his octopus (buddy had long since left him because of his fixation on his new toy). The diver admitted back on deck that he had not looked at his SPG during the dive.
The other two incidents were more "extremely low on air"; one was at 300 psi at 90 feet and the other was at 400 psi at around 70-80 feet. In both cases they talked after the dive of just following the group and assuming that everything was fine from an air standpoint and a nitrogen loading standpoint. Neither factored in their own air consumption by simply looking at their SPG. Going forward they were much better monitoring both psi remaining and nitrogen loading. As an instructor, these experiences created great teaching discussions. First, don't play with new toys until you are very comfortable with your abilities and, even then, don't let the toy distract you from your primary concern, air and nitrogen status. Also, just because all your friends jumped off a cliff, would you? In other words, what the group is or is not doing is not as important as how you are doing. Make sure you are always ok, then pay attention to the group so you don't get separated and you get to see the cool stuff they might see.
In short, all three were operator error in a big way.