Flush with cash, allied with Microsoft, growing exponentially, and positively humming with buzz, Facebook is definitely the "it" site on the Internet. Now what?

At the annual Foursquare Conference today, Facebook founder Mark Zuckerberg gave some hints about the future of the social networking phenomenon. He described its new advertising initiative, spoke of its relationship with Microsoft, and alluded to its budding rivalry with Google.

First, financing. C.F.O. Gideon Yu told Portfolio.com today that the company is preparing to raise an additional $260 million to close its Series D financing round.

"This will be the last time we take private money," Yu said, though he was quick to add that the company has "no plans to go public any time soon."

Next, features. Zuckerberg said that Facebook will soon be rolling out a new feature that allows users to choose what information they would like to share with different groups, such as business colleagues and personal friends.

During a question and answer session, Zuckerberg described the company's new advertising initiative, which he announced yesterday.

Among other things, it will allow businesses to set up their own Facebook pages and then reach out to real, live users -- that is, potential customers -- based on the interests they have described in their profiles.

If those interests include not seeing advertising, that is too bad. "There is no opting out of advertising," Zuckerberg said.

If it is any consolation, he added: "The ads are going to feel like content to a lot of people."

He also alluded to a budding rivalry with Google. Asked why Facebook chose not to participate in Google's new social networking consortium Open Social, Zuckerberg replied, "Who says we didn't choose to be a part of it?"

In fact, he added, "We didn't really find out about it until an hour after it launched."

Zuckerberg said it is "conceivable" that Facebook could seek to join Open Social in the future, but the company has no such plans at present.

"If it does really well, we may want to participate in it," he said.

At one point, Google co-founder Sergey Brin emerged from a side room at the conference, which was held at the Pierre Hotel in Manhattan, and headed straight for Zuckerberg. Bystanders held their breath, waiting for some kind of showdown.

But like a couple of championship boxers at a pre-fight weigh-in, they didn't so much as acknowledge one another. Brin just smiled as he walked straight past Zuckerberg, who kept his gaze straight ahead.

Describing Facebook's $240 million partnership with Microsoft, which includes an advertising component, the famously terse, frequently monosyllabic Zuckerberg said, "Microsoft does a lot of things that just make sense for us."

He said Facebook chose Microsoft as its advertising partner instead of Google, which has been much more successful at online advertising, for a simple reason:

"Not having done something before -- we don't see that as a disadvantage," he said, prompting laughter from the assembled media moguls.

Indeed, the lack of a track record has not hampered Facebook. Zuckerberg said the web site currently has 52 million active users, and is growing at 3 percent per week -- essentially doubling in size every six months. At that rate, he said, Facebook could have 200 million users by the end of 2008.

Zuckerberg said he personally spends about two hours per day on Facebook. "All of the people I know are on the site," he said, prompting more chuckles.

Asked if his parents were unhappy that he didn't graduate from Harvard before starting Facebook, Zuckerberg invoked Microsoft founder Bill Gates, another famous Harvard dropout. He, like Gates, could always return if business sours. "The good thing about Harvard," he said, "is that they let you take as much time off as you want."

After Zuckerberg spoke, Portfolio.com chatted with him and Yu as Steve Case, Harvey Weinstein, David Stern and others mingled about. [See event slideshow here.]

Yu, who was YouTube's C.F.O. before joining Facebook, described the "Valley ethos" shared by the two companies.

"There are these small bands of people who are trying to take over the world," Yu said. "This is so much more fun than working at a hedge fund or an investment bank."

by Sam Gustin

_{The full length video of Zuckerberg's presentation at the Foursquare Conference can be found here.}