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 Internet data center company 21Vianet Group, (NASDAQ:VNET) sank 10% today after its quarterly results and outlook disappointed Wall Street.

So what: The stock has soared over the past six months on signs of accelerating growth, but today's Q3 loss of $2.2 million, coupled with downbeat guidance, triggered concerns that expenses are increasing just as quickly. While revenue spiked 30% to $84 million, gross margin decreased 190 basis points over the year-ago period, suggesting that its competitive edge is getting more expensive to maintain. 

Now what: Management now sees Q4 revenue of $88 million-$90 million, below the average analyst estimate of $93 million. "[N]ew initiatives, such as our strategic joint venture with the Dongguan Municipal People's Government in Guangdong province to build a new Internet data center in southern China, will further help us to develop our cloud computing services as well as China's own interconnection market," Chairman and CEO Josh Chen reassured investors. "As China's Internet traffic and cloud services continue to grow, we are confident that our business model and on-going initiatives position us well to capitalize on future growth opportunities." With 21Vianet still up more than 100% from its 52-week lows and trading at a forward P/E of 30, however, I'd wait for an even bigger pullback before buying into that bull talk.