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 gaming operator Penn National Gaming, Inc (NASDAQ:PENN) fell as much as 10% today after releasing earnings.

So what: First quarter revenue of $641.1 million and net income of $4.5 million, or $0.05 per share, were in line with estimates, but the really bad news came with guidance. Management is seeing slow traffic in April and lowered full-year revenue guidance from $2.63 billion to $2.51 billion and net income from $21.9 million to $10.4 million. 

Now what: Increased competition from across the country is hurting regional gaming, and even Penn's own expansions will dilute results. This is just the latest data point that shows why investors should stay out of regional gaming stocks because Penn is actually one of the best-run operators. It's just not an industry I'd be willing to make a bet on right now.