Yes, I almost sliced off a piece of my right thumb (I'm left handed)with the original rotary cutters when I was making a boy doll for my then 2 year old son (he's 25 now). He was running around and I didn't pay attention to what I was doing. DH was at work. Luckily, our friend lived next door and took us to the hospital to have stitches put in my thumb. This occured before I started quilting.
Now, I use the retractable Olfa and still try to be very careful.