Yup. I did this once. I had $20 sitting on MtGox in a $1 buy order. Had a crash happened I would have picked up 20 bitcoins (which would now be worth around $50

Yup. I did this once. I had $20 sitting on MtGox in a $1 buy order. Had a crash happened I would have picked up 20 bitcoins (which would now be worth around $50,000). Instead MtGox disappeared, taking my money with them. Over a long enough time period, the risk of any given crypto exchange being hacked approaches 1.