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 health-care "payment management solutions" provider Emdeon (NYSE: EM) plunged as much as 10% this morning on the back of a downgrade to "market perform" from analyst William Blair.

So what: News that Blackstone (NYSE: BX) was interested in buying Emdeon for $3 billion drove up Emdeon's stock 22% in intraday trading yesterday. And rightly so -- if the rumors are correct, we're talking about a purchase price more than twice as high as Emdeon's current market cap.

Now what: But here's the problem: Emdeon's not worth $3 billion. Not even close. I mean, at $1.4 billion in market cap, the stock already costs nearly 65 times what it earned last year. Even if you value the company on its free cash flow, the $94 million Emdeon generated in "cash profit" over the past year prices this stock at more than 14 times FCF today.

Now, a multiple of 14 might be a fair price if Emdeon achieves the 14%-plus growth targets that Wall Street has laid out for it. But 28 times free cash flow? Seems a bit rich to me, and it seems William Blair agrees. My advice: If Blackstone is crazy enough to offer $3 billion for your Emdeon shares, take the money and run.

What will come of Blackstone's buyout offer? Add Emdeon to your watchlist and find out.