I came very, very, very close to cracking the core of a Duron 800 about 2 weeks ago. I was installing the HSF but I had the case rotated 180 degrees (so the the latch clip was closest to me) and when I reached about 18 pounds of pressure, there was a PLING! as the screwdriver slipped and the HSF rattled slightly off the socket.
It's a wonder that I didn't crack the core or pop a capacitor off!! Thank God that AMD puts those 4 pads on the corners otherwise it would've been a goner!
I slapped myself in the bald pate, rotated the case 180 degrees so that the latch was FARTHER from me (which is how I usually do it) because it gives me more leverage and with the dead weight of my upper body hovered over the case, it helps to slowly ease the clip down.