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 wallboard manufacturer USG (NYSE: USG) climbed as high as 14% on Wednesday after the company posted solid preliminary results for January and February.

So what: The huge year-over-year improvement -- $5.7 million in operating profit on sales of $516.9 million versus an operating loss of $46.8 million on sales of $446.9 million in 2011 -- is forcing analysts to raise their valuation estimates yet again. In fact, the shares are busting through their 52-week high on the news and are up a whopping 150% over the past six months alone.   

Now what: Expect the short-term sales momentum to continue. First-quarter results won't be out until mid-April, but management fully expects that March's results will also reflect higher wallboard prices and expanding gross margins. Given USG's still-hefty debt load and red-hot stock price, however, Fools should proceed with a whole lot of caution.  

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

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.