I think we have all had cuts on sharp computer cases. I have had two PSU explosions like Jory said. I think the worst thing Ive had was an electric shock (or a super nasty static shock) which strangely enough, came from a printer USB cable. I know it sounds like a lie since USB is only 5volts, and I have no idea how it happened, but I got one serious shock from it. The tip of my finger really hurt, my whole arm was numb for an hour and I felt the shock all the way into my chest.
The client was doing house renovations at the time, perhaps that had something to do with it. I really dont know what happened.