Postman- Unexplained, single-stock drops like DNDN's in April- 70% in two minutes during which all stops were taken out,then a trading halt, then a dramatic rise after the test results were announced- are more troubling to me than "whole market" glitches.
Mental stops are where it's at, IMHO. If one has a large amount of money in a stock and is not watching it carefully, then perhaps that person deserves what they get.