In the summer of 2006, CNN announced that it would dedicate a section of its website to user-generated video, audio, and articles in a new feature called CNN Exchange. The core framework was content-sharing — a “YouTube for news,” essentially — with CNN branding.

What began as something of an experiment is now a prominent feature of CNN, both online and on the air. CNN Exchange has morphed into iReport, and, today, the feature is celebrating five years of officially-recognized citizen journalism at CNN. And it suggests what might happen when user contributions to news organizations are approached in terms of scale: So far, iReport has attracted nearly 900,000 contributors worldwide; it garners an average of 15,000 contributions from them each month; its content nets 2.6 million views a month; and it’s been used to cover news events both breaking and non- — from the perspective, importantly, of the people experiencing those events first-hand.

“Our bet is: We don’t know everything; we don’t have all the answers, but we can probably collect more of them — and do more diverse, interesting, deep stories — if we ask for help and collaborate,” Lila King, CNN Digital’s participation director and the head of iReport, told me. “That’s certainly the leap we took when we launched iReport.”

iReport is celebrating today’s milestone with birthday features on CNN’s website, as well as in-person parties (organized by contributors via Meetup.com) in cities around the world. But as it does so, it’s also thinking about the next steps in its evolution. “If we get this right, the future of iReport is in more and deeper collaboration, among one another and also between CNN and the people it serves,” King notes in a blog post.

And that collaboration could have an even bigger impact on the coverage offered by CNN overall. In its five years, iReport has evolved from a classic content-sharing network — its first user contribution was a video of a squirrel — into a full-on reporting platform. An iReport from the scene of 2007’s Virginia Tech shooting provided audio of the events as they transpired. iReports from Iran were an important component of CNN’s overall coverage of the 2009 protests in the country. In the aftermath of the 2010 earthquake in Haiti, residents used iReport to post photos of missing friends and relatives and to ask for help in finding them. iReporters and CNN staffers have worked together, via iReport’s Open Stories project, to cover everything from the royal wedding to the Joplin tornado to the death of Osama bin Laden.

In its five years, in other words, iReport has evolved from a social network into a reporting platform. The next step, perhaps for the next five, will be figuring out how to be both of those things at the same time.