Pin Crowd

In the life of every enormously successful website, there’s a moment when it morphs from cult favorite into breakout hit. For Pinterest–a simple, image-centric social network suddenly enjoying a rush of mainstream buzz–that time is now, which means the going may soon get rougher.

So far, its rise has been meteoric. Pinterest launched in March 2010 and started to attract serious attention in Silicon Valley last year. In January, according to ComScore, Pinterest passed 10 million monthly U.S. visitors, reaching the mark faster than any other stand-alone site in history.

It accomplished this with a stripped-down visual twist on the now familiar share- everything paradigm of Facebook. As you come across interesting photos or videos online, you can use a special bookmark to “pin” them onto topic-themed “pinboards” you create. If you were remodeling your kitchen, for instance, you might devote a pinboard to appliances and cabinets that catch your eye. Pals could check out your choices, “repinning” their favorites and maybe helping your glass-tile backsplash go viral.

What else do people pin? Though you’ll find everything from vacation photos to infographics, fashion and decor images dominate, a phenomenon due at least in part to the fact that women are Pinterest’s most passionate fans. At least two start-ups, Dart It Up and Gentlemint, are working on sites that are essentially Pinterest for dudes.

For all its success, Pinterest is beginning to face tough questions. How will it make money? Has it been goosing growth by spamming members’ Facebook friends? Even the site’s premise, based on snagging images from all over the Internet, is being dissected because of copyright concerns.

“Copyright is a tricky issue, and we care about it a ton,” says Pinterest CEO Ben Silbermann, who notes that site owners can now lock down images so they can’t be pinned. As for Facebook, he says his company sends e-mails only to friends who have already joined Pinterest.

So much of the site is devoted to pictures of products for sale that some sort of e-commerce model seems inevitable. Until recently, it had been fiddling with links submitted by members so it could collect a finder’s fee from shopping sites when visitors bought products they found on Pinterest. (It says this was an experiment, now stopped, though the revelation raised a few eyebrows.)

Meanwhile, Pinterest mania is spreading to the corporate sector. Brands such as Lowe’s, Sony and Whole Foods are pinning their own goods to boards so fans can discover and discuss them. Which means Pinterest faces one more challenge: ensuring that it doesn’t lose the quirky, handcrafted feel that has attracted its huge following. For a site like this, bigger isn’t necessarily better. Sometimes it’s merely blander.

EXPLORE TIME’S PINBOARDS AT pinterest.com/time_magazine