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 management specialist Weight Watchers International (WW 3.31%) plummeted 26% today after its quarterly results and outlook disappointed Wall Street.

So what: The stock has plunged over the past several months on poor sales trends, and today's abysmal Q4 results -- earnings sank 47% on a revenue decrease of 11% -- coupled with downbeat guidance suggest that things are only getting worse. In fact, membership paid weeks, or global engagement, sank 8.5% over the year-ago period, reinforcing concerns over rapidly increasing digital calorie-counting competition.

Now what: Management now sees full-year EPS of $1.30-$1.60, well below the average analyst estimate of $2.78. "In Q4, we performed in line with our expectations," President and CEO Jim Chambers said in a statement. "While we are confident that we are on the right track to execute a successful transformation, 2014 will be a very challenging year." Of course, with the stock now off more than 50% from its 52-week highs and trading at a price-to-sales well below 1, those challenges might already be baked into the valuation.