AUSTIN, TEXAS (Fortune) -- We've all been there: the dull business conference. A half-empty room of half-asleep attendees answer their e-mail on laptops and BlackBerries, while some hapless speaker lumbers through a PowerPoint speech.

That scenario is about to change, thanks to the growing ubiquity of social media. Consider author Sarah Lacy's disastrous interview of Facebook founder and CEO Mark Zuckerberg at the annual South by Southwest Interactive Festival here. Lacy, a Business Week columnist and author of a forthcoming book on Zuckerberg and other Web 2.0 titans, drew the crowd's wrath by asking Zuckerberg too many questions about his age and his company's outrageous $15 billion valuation and not enough questions about issues more fundamental to how Facebook operates - things like trust, privacy, and accessibility to software developers. On top of that, Lacy interrupted Zuckerberg, seemed to flirt with him, and then grew hostile as the crowd turned against her.

And did it ever turn. Many in the audience started posting their thoughts on Twitter, a service that broadcasts instant messages, and the ire built. The crowd began hooting and jeering, and finally, when she opened the mike to questions, the first person asked Zuckerberg: "Other than rough interviews, what are some of the biggest challenges Facebook faces?" Lacy turned to Zuckerberg, asked, "Has this been a rough interview?" and the audience member said, "I wasn't asking you, I was asking Mark." The crowd went wild.

A bitter Lacy said she saw in the debacle "the downside of Web 2.0," but many others see it as a signature moment - for what it says about the coming wave of new media, for what it says about the way attendees can take over conferences, and even for the signals it sends about the still rising tide of people power that Web 2.0 has unleashed.

There were many similar episodes at this year's SXSW, a conference packed with folks empowered by their own mini-media empires on Flickr, Facebook, YouTube, Blip.tv, Twitter, Utterz and a host of other tech sites. Several attendees told of being in smaller panel discussions in which people either twittering or commenting in chat rooms run by social networker Meebo turned the conversation into a new direction.

In one, "a revolution in the chat room tore apart the panel," according to Forrester analyst Jeremiah Owyang. One person finally stood and requested permission to ask a question. "They said 'No',"Owyang recalled, "and he said, 'The whole room is behind me. I'm going to ask it anyway'." When the panel, on "Social Media Metrics," started to drag, according to Dave Evans of Digital Voodoo, a social media consulting firm in Austin, "you could see the laptops flip up and see the twitters happening." The panelists saw they were not giving the information that the audience wanted, and refocused the presentation, Evans said. "It was a really interesting collision between the Twitter back-channel and the live, public-facing channel," Evans said. "We always say that the crowd is taking control in a marketing buzzword kind of way," Owyang said, "but now it's actually happening."

This movement - call it Conference 2.0 - has been building for some time. Signs have been popping up in various places:

* The "un-conference" model, in which people show up for a conference and the participants pick the agenda and run it in an "open space" model. The most prominent of these has been tech publisher Tim O'Reilly's Foo Camp, in which a select crowd spends a weekend camping out in O'Reilly's offices in Sebastopol, Calif.; and barcamp, a more grassroots effort that sprang up in response to Foo Camp. Scores of barcamps have been held around the world in the last year and a half.

* The "lobbycon" phenomenon, in which people don't pay to go to conferences, they just show up and network in the lobbies. This is particularly big at Web 2.0 and other Silicon Valley events. Why pay top dollar to hear a sponsored session when everyone you want to see will be hanging out in the public areas for free?

* The "panel picker," an online forum that SXSW uses in which people suggest panels and then the community votes on what they want to see. The winners get to present. At this year's festival, about 130 of the 150 panels were chosen this way.

* Parties 2.0 - a big draw at SXSW is the parties, but now that attendance is pushing 8,000, some of the bashes feature insane lines. When the Google party was too packed to get in, tech bloggers Robert Scoble (who does Web broadcasts for Fast Company) and Scott Beale of San Francisco Web hosting firm Laughing Squid first twittered that the line was ridiculous, and then twittered that they'd start their own party at another bar. They called it the Alta Vista party and in half an hour had about 100 people.

"The entire un-conference movement started from the frustration with terrible interviews and terrible panels," said Chris Heuer, a social media consultant in San Francisco who has run his own un-conferences, such as Web 2.1, which he runs for free during the high-priced and exclusive Web 2.0 conference. "People finally feel empowered to take control."

Heuer recalls attending an AlwaysOn conference at Stanford University a few years ago in which the organizers had chat rooms projected onto a screen behind the speakers. "The value in the chat room was greater than what was being said on the stage," Heuer said. "People now have a voice, enabled by technology, to participate and be heard, and they're going to use it," Heuer said. "This has only just begun. It's only the first inkling of how people are going to seize the power from institutions. People in power need to find ways to get the audience to participate."

Dave McClure, who runs conferences including the Web 2.0 Expo and Graphing Social Patterns for O'Reilly Media, said the change is healthy. "I don't feel threatened by it at all," he said. "If you're watching what's going on in Twitter, you get a lot more feedback, and you can run a much more interesting session. People might want to be more on their toes understanding what the audience wants."

For his part, Zuckerberg had said from the stage how proud he was that Facebook had helped people in Colombia organize in massive demonstrations against their country's civil strife. He clearly heard the message, though, from his own acolytes in the SXSW ballroom. After his keynote debacle, he announced he'd have an informal question and answer session the next afternoon. About 200 people packed a bar where Facebook had been hosting a "developers' garage," and Zuckerberg fielded questions on everything from his personal life, to when he'll open up things like Facebook's friend lists to outside application builders.

"Yesterday's Q&A just wasn't enough fun," he said, somewhat in jest. He has refused to fault Lacy's questioning, instead taking heat himself: "We just didn't open it up to questions early enough. People at this conference are more interested in the policy and the platform." One attendee told him, "We give you props for doing that." The people were heard.