I personally waited 200km (130miles?) before I dared transporting my laptop in my backpack. I now have close to 4 times that under my belt, but i'm still extra careful when i'm carrying something fragile: take it easy, keep it simple, enjoy the ride...
When i start getting too playful, falling (and rolling on my back) does (rightfully) happen. It wouldn't be fun if you got all the tricks on the first try. ^^
For the record, i've never experienced any high-speed nosedive (my top speed is a safe 17mph). Since I'm experienced enough to understand what happens when I fall, I haven't had any unexplained nosedives of other sorts (i did have some).
At first, I would crash and my mind would kind of blink and get back to consciousness when i'm on the ground; It would all happen in an instant and leave me with very few clues. As i got better, time started to slow down and my mind was better able to understand and react to a fall situation; Also, my reflexes got better, so my body starts reacting early, moving back the moment i fall and giving my brain more time to process and react.
Anyway, my point is: nowadays when i fall, i always understand ultimately why. Even when i fall because of the board, it's because i hit a limit i knew about and should have avoided. For example, I fell on a tail-slide over-regeneration some days ago and the alarm started ringing when my ass was on the ground (perhaps there was a Bluetooth hick-up?). Still, totally my fault: new place, jumping fast down a steep hill with a full battery and braking hard when it gets steeper... Duh. What was I thinking? (I live on a hill, i battle with over regeneration everyday).