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 mail-based marketing specialist Valassis Communications (NYSE: VCI) dropped as much as 10% in early trading today on very high trading volume.

So what: Hurt by the bankruptcy of a large client, Valassis missed analyst targets and its own guidance in this morning's fourth-quarter report. Moreover, the earnings forecast for 2011 came in below the Street's consensus.

Now what: The company has come a long way from teetering on the edge of bankruptcy in 2009 and is doing a fine job of restructuring its formerly crushing debt load. But Valassis is subject to the vagaries of a fickle market; junk mail marketing (to be blunt) can ill-afford large setbacks as it runs on vanishingly thin margins already. If you bought shares for less than $2 each in 2009, congratulations; but the long-term prospects for this company and its general market look grim.

Interested in more info on Valassis Communications? Add it to your watchlist.

Fool contributor Anders Bylund holds no position in any of the companies discussed here. 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 is investors writing for investors.