Most significantly, some 39% of the May visitors were over the age of 35.

With a little more than half of the May users (13.5 million) over the age of 25, marketers may start to view Facebook as a social medium that can target a broad base of consumers, not just the college demo. Both the adult (25-34) and tween (12-17) age segments saw triple-digit growth, with surges of 149% and 181% respectively.

Facebook currently offers targeted banner ad, e-flyer, and forum sponsorship opportunities, and in late May, the social network opened up its platform code to developers and advertisers.

Since then, some 65 companies including Microsoft, Amazon and Red Bull have created viral, user-beneficial applications like games and widgets that also serve ads and conduct transactions - without having to share any revenue with Facebook.

Many industry analysts saw the move as a step toward making Facebook a more viable advertising channel, as banner ad click-through rates reportedly averaged 0.04% -- less than half of its rival MySpace's 0.10% -- according to the Valleywag tech blog.

ComScore's traffic reports for the months to come will likely yield insight into whether the shift in user demographics and open-sourcing will be a boon or bust to Facebook's members and the advertisers seeking to reach them. According to a comScore analyst, "We're not in the business of making predictions, but marketers can see that there is clearly a marked increase in traffic and unique visitor growth to Facebook."