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 regional bank stocks like Regions Financial (NYSE:RF), SunTrust Banks (NYSE:STI), and Zions Bankcorp (NASDAQ:ZION) all sank about 3% today on the Federal Reserve's move not to wind down its bond-buying program this month.

So what: The sector has soared over the past year on the expectation of steadily rising rates, but Fed Chairman Ben Bernanke's decision not to taper is prompting investors to take some dough off the table. After all, regional banks benefit greatly from higher rates because they charge more for loans, so the Fed's surprise move suggests the group will be posting lower profits and for longer a period of time than Wall Street had expected.

Now what: I wouldn't be so quick to play the regional banks for a short-term rebound. Even with today's decline, the SPDR S&P Regional Banking ETF is still up about 35% over its 52-week highs, and there's no guarantee the Fed will start to taper anytime soon. Of course, for conservative Fools with some patience, today's pullback might be providing an opportunity to scoop up some larger, less interest-rate-sensitive -- and therefore less risky -- regionals like U.S. Bancorp and BB&T for the long term.