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 consumer-review website Yelp (NYSE:YELP) soared 20% this morning after its quarterly results and outlook topped Wall Street expectations.

So what: The stock has rebounded sharply in 2013 on strong mobile growth, and today's second-quarter results -- loss narrowed to $0.01 per share versus a loss of $0.03 a year-ago on 69% revenue growth -- coupled with upbeat guidance only reinforces that momentum. In fact, about 40% of Yelp's local online ads in were on mobile handsets -- up nicely from 36% in Q1 and 25% in Q4 2012 -- while monthly unique visitors jumped 38%, suggesting that its market share continues to grow at a particularly rapid pace.

Now what: Management now sees full-year revenue of $222 million-$224 million, versus the consensus of $219.8 million, and EBITDA of $27 million-$28 million. "As we look to the rest of the year, we will continue to focus on driving innovation in mobile, integrating Qype, and closing the loop with local businesses," said CEO Jeremy Stoppelman. Of course, with the stock now up a whopping 200% over its 52-week lows and trading at a price-to-sales multiple over 15, much of that bullishness might already be baked into the valuation.

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