This post has been updated.

Facebook CEO Mark Zuckerberg speaks during a question and answer session at the TechCrunch Disrupt conference in San Francisco, California, September 11, 2012. (BECK DIEFENBACH/REUTERS)

The Facebook CEO sat down Tuesday evening for his first interview since the company’s initial public offering in May. During the sit-down, Zuckerberg acknowledged the stock price’s decline, expressed his regret over “betting too much on HTML 5” and emphasized that the company was looking long-term — three to five years — even as the market reacted as soon as the 28-year old CEO started to speak.

But the last question from TechCrunch founder Michael Arrington stood out: “Are you still having fun?”

Fun. The view of Facebook as an innovative company has largely centered on the idea that it is exactly that: fun. It is a place to work and have fun (take the company’s “hackathons” for example) and a site to visit to have fun — fun with friends, fun with family or even fun with perfect strangers. But, by asking if Zuckerberg was still having fun, Arrington cut to the heart of something important about how the company is seen in terms of its ability to innovate.

What happens, say, when Zuckerberg stops having fun?

He insists he still is, although immediately afterward said, “For me, it’s not about fun, though, it’s about mission.”

And during the interview, Zuckerberg appeared nervous — a warranted reaction when the stock-price of a multi-billion dollar company hangs on your every word. (Disclosure: Washington Post Co. Chairman and chief executive Donald E. Graham is a member of Facebook's board of directors.)

“It’s a coming of age for Zuckerberg,” said Post columnist Vivek Wadhwa during a phone call Wednesday.

“I’ll bet you he grows up 10 years this year,” he continued. “I would say his best days [at Facebook] are behind him.”

But, as Zuckerberg noted later on in his reponse to Arrington’s fun question, “I would rather be in the cycle where people underestimate us.”

And, according to Zuckerberg “a bunch of people” are doing just that, and it can be pretty fun to prove people wrong.

What do you think: To what extent are fun and innovation intertwined, and do you think Facebook is still a fun company? Let us know in the comments.

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