I cant think of turbulence without thinking of Foster Brooks as the drunk airline pilot..... https://m.youtube.com/watch?v=eC5_W_YsPKg
Absolutely! When I'm on an airliner and the seatbelt sign is on, I take that seriously. Almost always, those injuries are people who are not belted in (frequently flight attendants, who are doing their job). That said, the airplane is in no danger.
I think the airlines changed there safety message to 'keep your seatbelts fastened whenever you are in your seat' due to the fact that clear air turbulence is an unexpected event and the seat belt sign could very well be off.
My worst ever was NYto Flt Laud. about 15 years ago. It also happened to be the first time my m in law ever flew. The evening prior we had a major Nor'easter and the winds were crazy. The pilot made an announcement that said to those of you that are familiar with our normal route today will be very different. We will not be flying above 20000 feet for much of the flight, we will have some very moderate turbulence, we will not have cabin service and our flight will be several hundred miles inland instead of our usual hug the coast flight plan. Well they were not kidding, this was a rough flight that finally smoothed out once we got to the Georgia area. The funniest part of it was that when the flight smoothed out my m in law asked my wife if everything was ok. She thought the first part of the flight was the way it was supposed to be. We were hysterical.
On a B-24 flight to Pinecastle Airbase from Langley Field we passed under the anvil head of a huge storm off of the coast of North Carolina. No turbulence where we were but we could see the turbulence and lightening in the buildup. Awesome power was obvious.
If you ever saw what Boeing does to a new wing design and how far they have to flex them to make them intentionally fail, you wouldn't worry about turbulence. Just keep your eyes peeled when it gets rough in case a snack cart or flight attendant gets airborne.