The great breakthrough of the social web is that you can be known. That tangle of relationships that ties you to your identity offline is increasingly approximated online, and web sites from Amazon (AMZN)  to Zynga invite users to log on with social networking handles in order to interact with their real-life friends and colleagues. So it’s curious that the web site to capture the zeitgeist of our times is Chatroulette, an anonymous video site that requires no log-in. To play, you just go to the site, click a button, and talk to a stranger (or whatever else you want to do, just don’t tell me about it).

Chatroulette has the trappings of every web site fad. The site had 3.9 million visitors in February according to Comscore, quadrupling its traffic in a month. It has become a pop culture phenomenon with singer Ben Folds incorporating it into a live concert and Daily Show host Jon Stewart dedicating a segment to it. It has created at least one web celebrity, pianist Ben Merton who posts his improv videos using the site. It even has its own vocabulary word: players “next” each other when they’re ready to move on to a new conversation.

Meanwhile, site founder Andrey Ternovskiy, a 17-year-old Moscow high schooler, is entertaining funding offers from investors across the valley and in New York and considering a move to the United States. And enterprising web marketers already offer their clients Chatroulette advertising strategies, despite the porn that pops up.

So why do people like it so much? In many ways, Chatroulette delivers on the original promise of the web. On the Internet, according to the 1993 New Yorker cartoon, nobody knows you’re a dog. One of the chief draws of the web has been the anonymity that allows for creative expression of any whim or fantasy, regardless of how well it matches with our perceived identity. This idea of an identity has always been both liberating and constraining. As long as humans have existed, we have sought anonymous outlets for expression of thoughts and feelings that can’t be revealed without compromising the identities we have constructed for ourselves. Consider Mad Men character Don Draper who is married to his wife Betty, but has a series of extramarital affairs that must be kept secret because they’d compromise his identity as a loving husband and father.

Social media is sucking the secrets out of our thoughts and actions. For the most part, this is a great thing.  The social graph–that term coined by Mark Zuckerberg to describe the web of relationships that helps guarantee we are who we say we are–makes nearly everything better. Games are more fun because we know the players in real life. Books are more alluring because they come recommended by friends. And it’s more interesting to comment on Fred Wilson’s blog at Avc.com because you can identify the other people with whom you are conversing.

But we’ve taken identity to the extreme. We aren’t just constructing Facebook profiles anymore. We are building our personal brands, layering on photographs and compiling status updates that represent not the life we experience, but rather the life we want our audiences to believe we experience. And as more and more web services are launched and stitched together, allowing us to capture every image and identify our every location, we must complete an increasingly complex calculus to maintain these personal brands.

It’s no surprise that a backlash is emerging. My friend Guy Martin calls it Facebook fatigue. Last April when I interviewed Martin, 19, about how he used Facebook, he said he couldn’t even count how many times a day he went on it.  This week he told me he has temporarily deactivated his account. “I just want to connect with people,” he told me over a game of Scrabble. “I can’t stand people knowing all these things about me but not really knowing me.”

Chatroulette is the ultimate expression of that backlash. With the service, we divorce ourselves from the social graph and all the constraints of identity that it entails. We are free to click through other human beings much like we’d click through web pages. Sure, this freedom allows for a lot of penises. I played for ten minutes this morning, clicking through 20 rounds of videos and I saw four of them. It’s also boring; I saw 11 young guys sitting at desks with bland facial expressions. And it’s weird. A boy no more than 13 tripped around a den wearing a woman’s dress and high heels. But that’s why it’s popular, and why we play: in the lives we curate and broadcast on the web, we work hard not to be perverse, boring or weird. But these human expressions can, in their banality, be profound.