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 casino operator Boyd Gaming (NYSE: BYD) surged as much as 15% in intraday trading Tuesday after Merrill Lynch upgraded the stock to "buy" from "underperform."

So what: Citing a Las Vegas market that seems poised for a multiyear cyclical recovery, Merrill offered a $16 price target with the upgrade, representing 45% upside to Boyd's closing price Monday. Not surprisingly, Merrill also upgraded MGM Resorts (NYSE: MGM), whose shares are up 5% today, on those same Sin City tailwinds.  

Now what: I'd remain cautious about buying in right now. Boyd certainly stands to benefit from a continuing recovery in Las Vegas, but Asia-exposed casinos like Las Vegas Sands (NYSE: LVS) and Wynn Resorts (Nasdaq: WYNN) still strike me as tastier opportunities. And with lower debt-to-equity ratios than Boyd, they both seem like safer bets, as well.

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