It's tempting to buy a hot stock just before the company releases earnings. If the results and guidance are strong, you might get an immediate payoff. But American Eagle Outfitters (AEO) and Qihoo 360 Technology (QIHU) underscore that successful investors must be aware of the downside risks. Youth apparel chain American Eagle and Chinese online security and search firm Qihoo are selling off hard in the stock market today following their earnings