Yeah, I never really considered the hazard of the fixie either until I saw some of the threads. I used to get that rear wheel really spinning with the cranks then mess with a rag around the hub axel to clean out gunk. With the inertia of that wheel though, if you inadvertantly get a finger caught between a tooth and the chain, it's not stopping at that first tooth like with a freewheel - your finger is going around for the full ride. Knowing that too many fixed riders are missing some portion of their finger(s) keeps me careful now.