Is Microsoft (Nasdaq: MSFT) about to make an even bigger mistake than potentially overpaying for Yahoo! (Nasdaq: YHOO)?

Reports last week indicated that Microsoft bankers were sniffing around Facebook to see whether it was available after the Yahoo! talks began to break down.

I'm not suggesting that Microsoft is headed for a second bum steer. Facebook is the Lamborghini of social networking sites, and Yahoo! is stuck in an elementary-school speed zone. I just fear that a desperate Microsoft will pay too much, even for a speedster like Facebook.

Back in October, Microsoft paid $240 million for a 1.6% stake in Facebook. Financial journalists, who should know better, quickly whipped out calculators and arrived at the bogus conclusion that Facebook was worth $15 billion.

It wasn't. It isn't. Microsoft would be unlikely to shell out that much for the entire company. Along with its stake, Microsoft locked up multiyear rights to serve its ads throughout Facebook's site, globally. It was a cover charge, a ransom, but never the basis for an actual purchase.

There's a Zuckerberg born every minute
Don't get me wrong. Facebook would look great on Microsoft's arm. Facebook expects revenue to more than double this year to between $300 million and $350 million. Traffic at the website has more than tripled over the past year, according to comScore, to 109.2 million visitors in March.

When you're a traffic-hungry Microsoft, Facebook is delicious. You just need to eye the prices on the menu before you sit down to eat.

There will be a problem if Microsoft begins to believe the headline hype about Facebook's $15 billion valuation without acknowledging its role in generating that myth by its mutual back-scratching of a minority-stake purchase.

What is Facebook worth? Three of us Fools volleyed that question about three months ago. We were all over the map. Anders Bylund figured that it would be valued in the hundreds of millions in a few years. Tim Beyers said $15 billion is possible if "Facebook is as for real as we all seem to believe." My dart landed on $3 billion, based on a slight premium to industry revenue multiples. Yes, Facebook is growing quickly, but it's also toiling away in a fickle space.

Perhaps this is why I'm surprised to see Microsoft nibbling at all. CEO Steve Ballmer called social networking "faddish" a few weeks before the Facebook investment. If he believes that Facebook's popularity will fade after a few months -- or even a few years -- there's no need to whip out the money clip. Why buy the cash cow, when it's already drinking the online advertising milk for fee?

MySpace is your space
 Google (Nasdaq: GOOG) is still licking its wounds after its three-year deal to serve ads through News Corp.'s (NYSE: NWS) MySpace proved too tricky to monetize. Even if one argues that Facebook is growing at MySpace's expense, is there any reason to believe that Facebook's moment as everyone's darling will last much longer?

Facebook CEO Mark Zuckerberg is amazing, I'll admit. The media knocked him for his cocky ways a couple of years ago, and I know I've got some crow on my chin after ripping the company two years ago, when it walked away from Yahoo!'s alleged $1 billion offer.

But while Zuckerberg may be young, he's not stupid. Walking away then was the right thing to do. He has since convinced several Google execs to come over, so obviously, industry insiders see greater growth potential for Facebook. Zuckerberg always seems to be on the leading edge of Web 2.0 innovations, whether it's opening up the platform to third-party developers or the controversial yet intriguing social ads push.

In short, Facebook is unlikely to cash out cheap. Microsoft has a three-month migraine for pursuing a company that thought it was worth more than what the market dictated. Imagine how much harder it will be to keep that ego in check if Mr. Softy pursues a fast-growing privately held company that doesn't have the public markets to set a price.

Buy or die
Microsoft needs to go shopping, now that it can't bank on growing organically in cyberspace. It still has to check the price tags, though, even if its coffers are brimming with $26.3 billion in greenbacks. It saw what happened to its stock on dilutive Microhoo fears. The company needs to pick battles it can win, at attractive price points.

If it wants to shore up its online advertising backbone, a display heavy like ValueClick (Nasdaq: VCLK) is practically begging for an exit strategy. If page views are the name of the game, sticky sites like Wordpress, Ning, Marchex (Nasdaq: MCHX), or Internet Brands (Nasdaq: INET) can probably be had at attractive price points. 

There is no point in wasting time chasing private companies like Facebook and Digg, where Microsoft already has active ad-outsourcing relationships. The key is to swipe third-party publishers that currently ride on the Google and Yahoo! gravy trains. It also wouldn't hurt Microsoft go for high-value traffic, like Internet Brands' properties in automotive and travel, or Marchex's local search strengths.

You don't have to be a groveling sugar daddy, Microsoft, but you should definitely hit that online dating circuit with aplomb.