A lot of people think of stop orders as a risk mitigation method but I think in today's markets, stop orders are a bad idea. The only "normal" investors I know who have been hurt by flash crashes are people who use stops.
The issue there is that in a fast moving market, you might not get filled. When the stop triggers, the order "becomes" another limit order in the limit order book, and if the market's already moved bellow your limit, you dont execute.
Also, Market Orders are ALWAYS executed before limit orders, even if the limit makes it executable. That's just the priority system of the market.
In the continuous market time priority rules. If a marketable limit order arrives before a market order, the limit order executes first.