you know, it always makes me feel a bit better when I read stuff like this. I've broken bolts off on cars, snapped seatpost bolts from over tightening, put X doohickey back on when I should have put T, U, V and W beforehand, making me take it all apart again....I consider myself somewhat mechanical but with a dash of blunderer thrown in for good measure.

ps, for the record I have never broken off the top of a valve stem ;-)

pps, I recall lending my zefal to a guy who pulled up beside me on a bike path out on the island where the F1 track is here in Montreal. His rear tire was super low so I offered my pump. He stuck it on and with his furious pumping, rocked his bike back and forth enough to topple it over from his kick stand. With a mouthful of food I couldnt get the warning out in time, and he didnt move the pump as the bike went over, so off ripped his stem. I didnt have the right spare tubes to lend him, so the poor guy had a long walk ahead of him.