FAA statistics show that on average US airliners had about 190 turbulence incidents between 1980 & 2004.
In  most of these cases there were some injuries involving bruising during the flight. However, some injuries
are worst for example, on a recent Continental flight out of Houston Flight 511 encountered some rough turbulence                              in cruise flight. Most of the passengers sat down immediately.                                                                                                                       However,one passenger a lady in the bathroom was a little too slow returning to her seat. She was seriously hurt
suffering a broken neck that left her paralyzed. She remains in a Mc Allen, Texas Hospital. Pilots should be trusted
when we put on the seatbelt sign. Too many time I see people take their time returning to their seats.                                                Some people totally ignore crews request to return to your seat. Passengers must understand that the crew have more  
current knowledge of turbulence reports & could see whats ahead. If you are in your seat already its still a good idea to
have your seatbelt on. Neck injuries are a common injury for people hit with turbulence. On average only 58
injuries from air turbulence are reported annually.