"If you look at what's happened on the Web over the last 5 to 10 years with Facebook and other services, we love to share," he said. "We love to talk about ourselves ... and we're obsessed with learning about other people."

But for some, he said, the real world can be like "some bizarre social network where every profile is a single photo." On Highlight and similar apps, profiles are meant to let users know if someone around them shares their interests and might be a fun person to meet.

"It's a big change in how the world works," he said. "It's hard for me to think of a bigger shift in how the world works, but it's not going to happen overnight."

How Facebook might use app

Facebook-owned Glancee was somewhat more limited, pinging users when people already in their other social networks, such as Facebook, Twitter or LinkedIn, are around.

But for the folks from Mark Zuckerberg's company, such an app could have another payoff. Literally.

It would provide Facebook with reams of new data about not just where its users frequently go, but where they are right now.

Facebook said it doesn't sell its data to advertisers. But it definitely leverages the data to help those advertisers target potential customers. It's not hard to envision ads showing up letting users know that there's a 2-for-1 drink special right around the corner, or that the restaurant next door has the best burger in town.

"They need to make money on mobile, and that's what they've been pushing for since the IPO," said Justin Lafferty, co-editor of AllFacebook, an unofficial Facebook blog. "They're trying to build the technology first, then maybe find out how to build ads into it, too."

Lafferty, who wrote about this week's Bloomberg report, said Facebook could launch a social discovery app separate from its main mobile app -- at least at first.

"That's sort of how Facebook usually works," he said. "They'll test features, then they'll implement them all in the native app."

How will users react to such an app, were Facebook to launch one? Privacy advocate Polonetsky said that remains to be seen.

"The reality is that, for most people, even if things are broadcast to all their friends and the public, they still have some expectation about the way that it's used," he said. "I totally get that my neighbor knows when I come and go and may even say, 'We haven't seen you in a while -- is everything OK?'

"But if someone else seemed to know about my comings and goings and offered me a product or service based on it? I don't know."