By Tomio Geron Facebook employees celebrated the company's initial public offering in the company's traditional wayâ¿¿an all-night hackathon. But after a quick bell-ringing ceremony the company went back to business as usual. David Sze, partner at Greylock and an early investor in Facebook participated in the celebration. He stopped by Facebook's hackathon Thursday nightâ¿¿he acknowledged being up most of the nightâ¿¿and then came to Facebook headquarters for the Nasdaq bell-ringing ceremony at 9:30am ET. The ceremony took place in the central square at Facebook's new campusâ¿¿the former campus of Sun Microsystems. The excitement and energy were high, Sze said in an interview at the company's Menlo Park, Calif. headquarters. "People were milling around in the middle of the square in anticipation," Sze said. "(COO) Sheryl (Sandberg) spoke a little bit. The (person from) Nasdaq spoke a little bit. Mark spoke. Then they opened the bell. Everyone cheered and celebrated for about 10 minutes. Then everyone went back to their offices and started working again. It's a great milestone for the company. Wonderful congratulations to all of them. But one of the great things about Facebook is you don't get to where they've gotten and get where they're going to go without being really focused." Sze, number four on the Midas List this year, invested for Greylock Partners in Facebook in early 2006, when Facebook was still a social network for co-eds only. That early investment, ridiculed by some at the time, is now worth well over a billion dollars and has made Greylock one of the high profile names in the venture capital industry. But the celebration didn't last too long, Sze said. "People were celebrating. They're happy. A lot of people were up all night hacking. They were showing off some really cool projects and the like. Once it was over, they went back to work. Very classic Facebook."