Forstner bits are great for drilling large holes neatly. As long as they are straight in the hole, they are fine, but if they get slightly off line, they can grab, with exciting results. If the hole is not very deep, they can jump out and go waltzing across the job (which is what I'm assuming happened with Terry's victim). If you're using a drill press, the job can act like a helicopter rotor, and if you're using a hand held drill, it can do a quick flick and sprain your wrist, as well as spinning the job if it's not clamped.
Good practice to always clamp the job down, and smear a bit of candle wax on the outside of the bit.