I've seen 2 people get their teeth broken. One was a hot AEG slightly over 400 and he was shooting his M4 like it was an m249( yes, he was an assh&?%) the other was around 380 if I remember so it was a legitimate accident.
My first rule is shhoot the freaking vest or legs. It's not good practice for real life situations but this is airsoft, I've gotten mouth and google shots too many times to know that it's just because of plain bad habits people take on.
The 10 feet rule is a farce. Shoot the freaking vest, I've shot people in the back or execution style and never hurt anyone of em juste because I dont shoot vital parts.
There are situations that will probably make you shhoot the person in the face though, like if it's the only target you offer, I dont see whhy I would'nt use it so in the end it's also about being comphrensive taht you must give and take, just like chrismas...except this one leaves a different mark on your heart :P
AIM FOR THE FREAKING VEST!!!