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 office supply retailer OfficeMax (NYSE: OMX) fell as much as 10.5% on heavy volume.

So what: The fourth-quarter earnings report looked just fine, beating analyst estimates on the bottom line and staying close to Wall Street targets in terms of revenue. The problem lies in guidance, where OfficeMax cautioned that lots of promotions will combine with a perennially unpredictable economy to put pressure on sales and margins in 2011.

Now what: The report also dragged rivals Staples (Nasdaq: SPLS) and Office Depot (NYSE: ODP) through the dirt today. Their reports are coming up over the next two weeks, and then we'll know whether the margin pressure is an industrywide phenomenon or OfficeMax's own problem. Keep in mind that OfficeMax gets the least respect out of the threesome from our CAPS system, scoring a rock-bottom single star since time immemorial.

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

Fool contributor Anders Bylund holds no position in any of the companies discussed here. Staples is a Motley Fool Stock Advisor pick. Try any of our Foolish newsletter services free for 30 days. 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.