I had a messenger-style bag I carried my 15" MBP in. One day, while walking to my car from my apartment, the loop that holds the shoulder strap came undone from the side of the case and the case plunged 3 feet on to concrete and dented the left hand side of the bottom casing.
When my GF8600 went bad, Apple wouldn't honor the warranty on it because it had been dropped. They wanted to replace the bottom casing, top casing/keyboard/trackpad, logic board, power board, screen casing, hard drive and DVD drive and charge me $1800 for it.
I said **** that **** and replaced the bottom casing and logic board myself for $350. I ended up replacing the top casing keyboard and trackpad because I wanted the newer model trackpad capable of gestures, not that it attered when Snow Leopard came out.