Facebook Inc. began trading today at $42 a share, 50% higher than the low end of the $28 to $35 range the company noted in a U.S. Securities Exchange and Commission filing earlier this month. That pricing puts the value of the company at $104 billion. As of

Facebook’s initial public offering could raise more than $18.4 billion, which would make it the biggest IPO in history for a technology company. Google Inc. raised nearly $2 billion when it went public in 2004.

“The strong pricing indicates unabated, exuberant investor demand,” says Josef Schuster, founder of IPO research and investment house IPOX Schuster. “Given the big stock market slump across all market sectors during the past weeks, which is not reflected in Facebook’s share price, investors at these levels may be in for a rough ride for the time being.”

Facebook generates the vast majority of its revenue from advertising. In 2009, 2010 and 2011, and the first quarters of 2011 and 2012, advertising accounted for 98%, 95%, 85%, 87%, and 82%, respectively, of Facebook’s revenue.

Not everyone is convinced that advertising works on the social network’s platform. 44% of consumers say that they never click on Facebook’s ads, according to a new report by digital marketing agency Greenlight. And General Motors earlier this week said it would pull its ads from Facebook because of poor results.

However, GM’s issue with Facebook ads was that the social network doesn’t cater to direct response advertising, which seeks to drive an immediate action, says Susan Etlinger, an analyst at research advisory firm Altimeter Group. However, that doesn’t mean that Facebook ads don’t serve a purpose in marketers’ advertising portfolio, she says. “Brands have to take the long view,” she says. “They have to think about not only the requirements of advertising today, but what advertising will look like in five or 10 years. The brands that will succeed are the ones that take a holistic view of marketing in which they reach shoppers in different ways, depending on the platform.”

Retailers and brands have little choice but to continue experimenting with Facebook because of its massive scale, she says. Facebook has 901 million active users. “Are brands really going to miss out on the opportunity to reach those consumers?” she asks. “Social media represents a sea change in the way consumers and brands interact. So retailers not only have to think about how to sell stuff, they have to think about their strategy to incorporate customers and their friends and their friends’ friends into their sales strategy.”