At the Web 2.0 Expo in San Francisco on Thursday morning, as he prepared to interview Marc Andreessen, co-founder of social networking platform Ning, John Battelle, chairman and CEO of Federated Media Publishing, articulated the conference's collective angst about the Web 2.0 movement's future.

We're in "a time we're all questioning whether or not we can sustain the momentum," Battelle said, an acknowledgment of doubt that might not be so noteworthy were it not echoed in other presentations.

Tim O'Reilly, founder and CEO of O'Reilly Media and father of the Web 2.0 meme, posed a similar question at his conference keynote on Wednesday: "Do you really think we're done yet?" he asked. "I don't. I think we have a long way to go and a lot to discover."

One might write off such musing as a function of the flagging U.S. economy, but doubts could be heard at other conference sessions. A session on comparing the respective social networking development platforms on Wednesday revealed that we're in "a new territory and we're all going through it together," as Dave Morin, senior platform manager at Facebook put it.

Also on Wednesday, while interviewing Slide CEO and founder Max Levchin, Forrester analyst Charlene Li asked whether widgets were a fad.

Levchin at least mustered a spirited defense, saying, "No. It's the only thing that's going to prevent today's social networks from becoming fads."

Such doubt about the continued vitality of the Web 2.0 meme and movement can be attributed partly to uncertainty about the future of the Web browser, now that other devices are eclipsing the PC in terms of industry focus. Battelle revisited Andreessen's pioneering role in the creation of the Mosaic Web browser, which spawned Netscape and Firefox and made Web 2.0 possible, as if to reminisce about the good times before pondering the browser's demise. "Does it disappear over time?" he asked.

Andreessen said he had always assumed the browser was a halfway step and that it would just melt away. "The surprising thing has been the persistence of the browser as a distinct piece of software," he said, adding that more and more services, like instant messaging, appear to be moving into the browser.

There is of course no shortage of companies that would like to see the browser fade away so they could become more effective gatekeepers and reap the potential revenue that comes from being a gatekeeper. This desire explains the appeal of rich Internet applications, such as those developed with Adobe AIR, which gives application developers more control over customers.

Though Andreessen expressed surprise that the browser has lasted so long, he also appears to be aware of why the browser has lasted. Responding to Battelle's efforts to goad him to take a shot at Microsoft, his old adversary, Andreessen responded with praise for his nemesis during the nineties.

Bill Gates, Andreessen said, "made an unbelievable contribution to the industry. It's hard to imagine what this industry would be like if Microsoft hadn't standardized the operating system..."

The same might be said about Andresseen and the Web browser. Someday, a better standard platform for information retrieval may emerge. But since no one really know when that might be, it's probably safe to say that the Web browser, and by extension the precepts of Web 2.0, have years if not decades of life left.