My Macbook Pro in my leather case fell from the top of my suitcase at the airport, and still is going strong (knock on the wood). It was almost thrown out of one of those plastic boxes by a TSA officer at SFO airport, and still going strong...
I'd say, without trying, that my MBP is pretty durable. I may be nuts, but I believe that the 13' may be the most solid of the MBP line, because of its size...