Although we don't believe in timing the market or panicking over market movements, we do like to keep an eye on big changes -- just in case they're material to our investing thesis.

What: Shares of Chinese online video company Youku.com (NYSE: YOKU) plummeted 21% on Thursday after its quarterly results disappointed Wall Street.  

So what: Youku has been spending heavily to deal with increasing competition, but its third-quarter loss -- $7.4 million versus the consensus of just a $3.7 million loss -- is triggering fears that management is fighting a losing battle. Unfortunately, the pressure on Youku is coming from all sides of the profit equation, as rivals like Sohu.com (Nasdaq: SOHU) and Tudou Holdings have been pushing up licensing costs and making it difficult to keep customers.

Now what: For the fourth quarter, management now sees revenue growth of 90%-100%. That's obviously outstanding, but unfortunately represents, as fellow Fool Rick Munarriz writes, "a slight deceleration from its triple-digit pace of the past." When you couple ever-increasing competitive headwinds with the stock's still-lofty price multiples, it's probably best to stay on the sidelines.

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