It was a typically vexing week for Facebook. On the one hand, the social-networking service signed up its 500 millionth active user. On the other hand, it was found to be one of the least popular private-sector companies in the United States by the American Customer Satisfaction Index. Apparently, Americans were more satisfied filing their taxes online than they were posting updates on their Facebook page. It is a continuing contradiction: Facebook is widely criticized for shifting its terms of service and for disclosing private information -- and yet millions of people start accounts each month. Analysts always grasp for analogies to explain Facebook's tortured relationship with its users. Facebook has been called the sterile suburbs to the gritty urban Internet; it is a 'walled garden' in the organic messiness of the Web; it is Russia under Vladimir Putin; it is (and this one stings in tech circles) today's AOL. But perhaps the most telling metaphor compares Facebook to the other companies lurking at the bottom of the American Customer Satisfaction Index: cable companies, wireless telephone service providers, utilities. Here are services everyone uses, no matter how much people dislike the companies that provide them. Danah Boyd, a social media researcher at Microsoft and a fellow at Harvard University's Berkman Center for Internet and Society, argues that Facebook fits that mold. On her blog in May, she posted: 'I hate all of the utilities of my life. Venomous hatred. And because they're monopolies, they feel no need to make me appreciate them. Cuz they know that I'm not going to give up water, power, sewage, or the Internet out of spite. Nor will most people give up Facebook, regardless of how much they grow to hate them.' Boyd argues that even Facebook sees itself this way, describing itself as 'a social utility that helps people communicate more efficiently with their friends, family and coworkers.' The company's goal, Boyd says, is to become part of the infrastructure of the Internet. Utilities are generally subject to added levels government regulation because of their fundamental importance and tendency toward monopoly, so calling a company a utility comes with an uncomfortable implication. Mark Zuckerberg, Facebook's chief executive, was asked last week whether the company should be regulated, since he likened the company to an electric utility. He rejected the comparison. 'We're here to build something useful,' he said. 'Something that's cool can fade. But something that's useful won't. That's what I meant by utility.' Is Facebook important enough to be considered a utility? And is there no real alternative? Facebook is clearly not as vital as the electric grid. But many technologies now seen as essential were once dismissed as mere frivolity. 'At one time we could have had this conversation about the phone, and it would have sounded just as crazy,' said Christian Sandvig, an associate professor of communications at the University of Illinois at Urbana-Champaign. There is also debate about how firm a grip Facebook has on the market. Some experts argue that Facebook has grown so large that it is nearly impossible for a viable alternative to emerge, despite the presence of other social networks. Facebook gains data from each additional participant, growing more useful as it expands. This makes it progressively harder for users to leave, an economic principle known as lock-in. Giving users greater control over their own data would help offset this tendency, said Sandvig. Users could then take their personal information and social connections to competing sites, much in the way that cellphone users switch carriers without changing their phone numbers. Companies would be encouraged to offer alternatives -- stronger privacy settings or ad-free sites with paid subscriptions. But it is unclear how this would work. Even if social networking companies agreed to common standards that allowed a free flow of data -- or were forced to accept such standards -- there is no clear line between a person's own data and the data of the people in her networks. What right does someone have to her friends' data? There could also be unintended consequences. Treating a company like a utility, for instance, can help to lock in its dominance and discourage innovation. With this in mind, Cindy Cohn, the legal director of the Electronic Frontier Foundation, says that no one has developed the vocabulary needed to address social networking. 'I worry that we'll end up with solutions that are familiar but not correct if we start from the wrong metaphor,' she said. 'And I'm not sure there is a good metaphor for Facebook.' 