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 Weight Watchers International (NASDAQ:WW) plunged 20% today after the weight management specialist posted a disappointing second quarter, cut its full-year forecast, and said that CEO David Kirchhoff has resigned.

So what: The stock has been walloped in 2013 on disappointing recruitment trends, and the Q2 results -- EPS fell 15% year over year on a revenue drop of 4% -- coupled with downbeat guidance for the full year suggest that the competitive environment is only getting tougher. And while Weight Watchers said that CEO David Kirchhoff is stepping down to "pursue other opportunities," the surprise move doesn't exactly give investors a good feeling over the company's near-term turnaround prospects.

Now what: The company now sees full-year EPS of $3.55-$3.70, down from its prior view of $3.60-$3.90 and below Wall Street's view of $3.72. "While I'm excited about the team's plans for the January 2014 campaign, the 2013 recruitment weakness means that we'll start 2014 with fewer active members and therefore a lower earnings base," said newly appointed CEO Jim Chambers. "That said, I believe in our strategic potential and I am confident that we have the building blocks in place to enable a meaningful transformation over the next few years." More important, with the stock now off more than 30% from its 52-week highs and trading at a forward P/E of roughly 10, betting on that long-term improvement might be a decent idea.