OK, so most of you don't agree that social networker Facebook is worth $15 billion. So be it. I may, indeed, be wrong.

But I'm encouraged by the results of a new study from Microsoft (Nasdaq: MSFT) subsidiary Avenue A | Razorfish, which concludes that advertising dollars are moving away from portals such as MSN and Yahoo! (Nasdaq: YHOO) toward vertical sites, including social networks Facebook and News Corp.'s (NYSE: NWS) MySpace.

Digital ad dollars spent through Avenue A | Razorfish reached $735 million in 2007, up 36% from the prior year. Vertical sites accounted for 39% of that total, up from 37% in 2006. A "vertical site" attracts readers purely for its original content -- such as Fool.com. Portals and search engines, by contrast, aggregate information.

But it was the entertainment and community sites -- like Facebook and YouTube, respectively -- that saw the greatest growth among verticals. Each subset improved by more than 50%, to $51.5 million and $55 million, respectively.

Search engines also blossomed, with the likes of Google (Nasdaq: GOOG) and IAC's (Nasdaq: IACI) Ask.com improving their share of ad dollars from 28% to 31%.

Notice anything in the math? Verticals and search engines improved their share by 5% altogether. Portals dropped by the same amount; down from 24% in 2006 to 19% last year.

To me, this all but confirms that a Microsoft deal for Yahoo! would be, at best, ill-advised. Yahoo!'s properties are no longer the go-to spots to reach the digitally hip.

Facebook and MySpace are where it's at now. And while we've no proof that Facebook can produce the sort of revenue a $15 billion valuation would demand, it's become clear that advertisers covet the network it has built. Same with MySpace, LinkedIn, and each of their social-networking peers.

In short: You're yesterday's Internet, Yahoo!. It's Facebook that is the face of the digital future.

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Fool.com and Rule Breakers contributor Tim Beyers owned shares of Akamai at the time of publication. The Motley Fool's disclosure policy knows a deal when it sees it.