Dropped my first helmet off the tank at least 20 times before I learned not put it there... Still wore it till it got stinky beyond repair.
Then dropped a then brand spanking new AGV TiTech from the top of my car at around 20mph (you know the drill... put helmet on top the of the car, get keys, get in the car, completely forget about the helmet till there's a bend on the road) it cracked the paint job. I kept the helmet but never had the balls to wear it again... I only ride track and I need to feel 100% safe out there or it's just not fun.