Here's our Merc story today (free registration) on Facebook, the Web site that is all the rage on college campuses these days.

This site, for now, is rocking. From what we can tell, college students across the country are obsessed with it. Within just two years, Facebook (last week, it changed its name from Thefacebook, and redesigned its site) has signed up 3.65 million users, and last week half of them were signing in every 24 hours -- even though students are still on summer break.

So Facebook, like a few key other sites, appears to have discovered the magic recipe for success: Firmly rooting itself in the offline lives of its members. Facebook fans go to the site for daily activities like planning parties, finding the room numbers of classmates and just gawking at the lives of others. Here are a few more notes that didn't make it into the story:

We'll have more to say on Facebook within the next day or two, so stay tuned. Right now, MySpace is the other hot company that lets you connect with friends. Like Facebook, MySpace has been around for about two years, and has seen usership explode. Driven by music profiling and sharing, MySpace, of LA, has had an even quicker uptake than Palo Alto's Facebook.

In part, that's because MySpace hasn't limited itself to college students. Facebook requires you to have a university (.edu) email address. MySpace also gives you more freedom on the music sharing front. Here's a good story about MySpace that just ran in the NYT. Last month, Rupert Murdoch's News Corporation agreed to pay $580 million to buy MySpace's parent company, in part because of MySpace's demographic and reach. (We tried reaching them for comment on the Facebook story, but PR person was on vacation in Greece, so we didn't hear back. We'll give them a break, and not assume this is early celebrating.)

Facebook's 21-year-old chief executive, Mark Zuckerberg (picture here is courtesy of The Harvard Crimson), has a notable philosophy. He says part of the reason students have opened up so much to each other at Facebook is because of limits drawn. Students at other schools who are not your friends can't see your full profile. "Sometimes, by drawing boundaries, you increase the utility of this kind of site," he told us. "You can't give people as much power as they want."

Anyway, both Facebook and MySpace have surged ahead of the earlier players in the social networking area, including Friendster. (Friendster did not respond to a request for comment on the story).

We got some interesting insights from Facebook's Matt Cohler, 28, who runs daily operations. He believes Facebook will surpass Google in total page views by the end of this year -- or about 6 billion page views. And there's more. The NYT piece mentions that MySpace has already surpassed Google on this measure, and explains why this is so (users surf around more on MySpace -- and Facebook too -- whereas Google users usually go to Google, get what they want, and move on). Still, it is notable. While Google likes to poach the valley's best employees, Cohler says he's fighting back by giving prospective candidates another nugget to chew on: The engineering-leverage ratio. With 12 engineering employees, Facebook has about 3 billion page views, for a ratio of page views/employee of about 200 to 300 million. Google, meanwhile, has about 6 billion page views, with about 2,000 engineers, making for an engineering-leverage ratio of a mere 3 million. "We've got the highest page views per engineer in the world," crows Cohler. "That's the crux of the argument we have for making people come work for us."

Finally, one notable feature we didn't mention in the story is Facebook's "poke" feature, a whimsical feature for a user to let another student know they're interested in communicating with them. Zuckerberg joked that it is "worthless," and that he devised it as a way to bug his girlfriend. It is the sort of feature like Google's "I'm feeling lucky" button, that doesn't have much use, but reflects a playfulness, and creates a powerful viral affect among users, says analyst Standard & Poor's Scott Kessler. He says, of the Facebook: "It's 'the' resource college students have been using to find each other, communicate with each other."

It'll be interesting to see whether Facebook is just the flavor of the year, or whether it has real sticking power. In the story, we mentioned how advertisers already are interested in the Facebook's attractive 18-24 year-old college demographic. Kessler said the college demographic has limited its reach, which is true. But as we said, stay tuned...we'll have more shortly.

Our past coverage of Facebook here.

Update: Corrected some typos.

Update II: Some interesting thoughts here by Doug Sherrets.