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 gypsum materials maker USG (NYSE: USG) chalked up a big win today, gaining as much as 12% on moderate trading volume.

So what: The Commerce Department just reported the largest number of new housing unit starts in nearly two years, followed by more freshly issued building permits. That's great news for drywall specialists like USG and Eagle Materials (NYSE: EXP). Homebuilders Hovnanian Enterprises (NYSE: HOV) and Beazer Homes (NYSE: BZH) are celebrating this rare spot of good news with even larger share-price jumps.

Now what: The obvious question now: could this homebuilding rally be sustainable? The industry simply must bounce off rock-bottom at some point, and this could be it. I wouldn't take out a second or third mortgage to bet on that possibility, but homebuilders and their materials suppliers suddenly look interesting.

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