Earlier this week, we heard a vague promise from Pinterest's founder Ben Silbermann: The fast-growing social bulletin-board website would be adding user profiles by week's end.

Voila! On Friday morning Pinterest introduced profile pages that showcase a user's photo more prominently, as well as the other individuals that user most often re-pins. Those links provide something of a visual-social hierarchy, and allow visitors to easily witness who influences whom. 

The reasoning behind the change is simple, Silbermann said earlier this week at the South by Southwest Interactive festival in Austin, Texas. 

Over the past few months, Pinterest has popularized the Web concept of the "board," which looks more like a geometric grid, and visually presents and organizes user recommendations. It's quite a Web-design shift from a "real-time feed," a vertical list of text-heavy links a la Twitter, which has dominated online user-experience for the greater part of the past decade. 

"For me, boards are a very human way of looking at the world," he said. "Google's has always had tags in Gmail, but I've always loved folders, because they are…a way for me to make sense of the chaos. I think a board is…the same way."

The site already has more than 11 million monthly unique users, according to recent comScore data. It also keeps users reading and clicking around for nearly 100 minutes per month, which is more than LinkedIn or Twitter. So why the redesign?

"We wanted to make it more beautiful. And I know that probably sounds really generic…but we wanted to make your profile very, very different in kind from the profile you have on Facebook or the profile you might have on Twitter or your homepage," Silbermann said. "We want to be this snapshot of what you're about and we wanted to represent that visually."

Extending the visitor access to seeing top "influencers" of other users seems to be another effort to differentiate the way social networks form and spread on Pinterest, compared to the way friends are suggested on Facebook, say.

"A lot of the connections people have on Pinterest are their friends on Facebook, or people they follow on Twitter—but a lot of them are people they don't follow on any other social network," Silbermann said.

At first glance, new featured photos for a user's boards appear incomplete, and fit awkwardly into new, horizontal boxes, but the design is crisp, and allows casual pinners' boards to appear less like empty parking spaces.

The Pinterest team is also working to expand the number of people it reaches across devices—and although Silbermann didn't have a date for an iPad app launch: he said, "I can't wait to be using Pinterest on the iPad." 

It will all be built on a common API framework, so Pinterest will be stable across platforms. And Pinterest is planning on opening up its API to eager developers, too. 

"As a company, Pinterest itself has been a huge beneficiary of the APIs and the platforms other companies have created," he said. "So it just seems right to eventually find a way to open our API out."

Silbermann said his team has already been in talks with "a lot" of start-ups who want to operate within its API. The obvious question becomes: Which small companies are going to be to Pinterest what Zynga (the maker of Farmville) has been to Facebook?

One thing's clear: Silbermann isn't interested in foregoing the grid structure of Pinterest pages anytime soon. Simplicity and beautiful visuals are here to stay. "I want Pinterest to feel like a really human service, something that's really accessible," he said.

That stems from his original intent in building the site.

"I wanted to create a service that was a little bit timeless. If something is your favorite book, it's no less your favorite book 72 hours from now, a year from now, or five years from now, or 10 years from now."

Only time will tell.