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: Coinstar (Nasdaq: CSTR) dropped 10% in intraday trading today after guiding second-quarter revenue below expectations and announcing the departure of a key executive.

So what: Management expects revenue of $434 million to $436 million for the second quarter (which ended in June), below the consensus forecast of $446 million. The president of its high-growth Redbox DVD vending machine unit has resigned "to pursue entrepreneurial and other interests, and will continue to serve as president until a successor is named."  

Now what: EPS guidance of $0.96 to $1.00 for the second quarter and $2.90 to $3.15 for 2011 compares favorably with the consensus estimates of $0.81 and $3.02, respectively. But second-quarter revenue grew only about 27%, a marked slowdown. The latest guidance was buried in one of three press releases from the company, suggesting management was trying to slip one past investors. Guidance anticipates a record fourth quarter and appears to rely upon both the timing of new releases to Redbox kiosks and the planned deployment of Safeway (NYSE: SWY) coin kiosks that were announced in June. That's a lot of risk for a stock with slowing growth and a P/E ratio of 27 times after today's sell-off.  

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Fool contributor Cindy Johnson does not own shares of any company named above. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.