[Update, 9:21 a.m.: Facebook shares have settled in around $40/share, after opening at $42. Notably, shares of Zynga, the maker of blockbuster Facebook games, have plunged 13 percent today, and the NASDAQ is down slightly.]

Can Facebook hold on to its hacker culture as it becomes a public company? In the buildup to the social network’s closely watched IPO today, the people who work at the company seem to be doing everything they can to stay true to their roots.

After giving Mark Zuckerberg a standing ovation during a company meeting yesterday afternoon, Facebook employees participated in an all-night hackathon, where they build prototypes based on their ideas. The company explains on its press site, “Many of our most successful products came out of hackathons, including Timeline, chat, video, our mobile development framework and some of our most important infrastructure like the HipHop compiler.”

Employees at the company’s Seattle outpost, the largest Facebook engineering office outside of California, also took part in the event, with a printed curtain sent up from headquarters reading: “STAY FOCUSED AND KEEP SHIPPING.”

Mark Zuckerberg rang the opening bell for the NASDAQ stock market a short time ago from Facebook’s headquarters in Menlo Park. And yes, he was wearing his hoodie.

CNBC has a good live blog for tracking the events.

Here’s a collection of images including photos provided by Facebook and images from the NASDAQ live stream.

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