I've used my Delta Unisaw as a hobbyist for 10 years and never had a kickback--until yesterday.
I was ripping a piece of oak about 8 inches wide and 20 in. long. I was using a blade guard with integrated splitter and anti-kickback pawls. I had a horizontal featherboard holding the workpiece against the fence. The offcut was about 1/4 in. wide. The rip cut was complete and I was pushing the workpiece past the blade when I heard a loud whap! and felt something hit me me hard just below the belt. The offcut piece had been caught by the blade and turned into an arrow. I was only bruised but I know it could have been a lot worse.
Somehow the anti-kickback pawl was not properly engaging the offcut piece. The pawl is easily deflected sideways and an offcut piece only 1/4 in. wide can easily slip to either side of the pawl, entirely escaping it's grip. The offcut piece must have flopped around enough to get caught by the blade. The workpiece between the blade and the fence remained where it should be.
I'm not sure what to do to keep a thin offcut piece from getting caught by the blade but I've learned two lessons:
1) Like the safety books say, keep your body out of the plane of the blade. I usually do this, but "usually" doesn't help when kickback happens.2) Accidents can happen when you least expect it. Just before I started the cut I thought "This cut is properly set up--lots of safety here." I felt safe, but breaking one safety rule is all it takes.