It seems like more people today keep in touch on social networking Web sites than they do anywhere else: They can e-mail, chat, play games, post pictures and more. Social networking sites are a curious example of the Internet as a growing industry because most of the sites, such as Facebook and MySpace, are free for users but still designed to make a profit. They are always looking for creative ways to build revenue, and sometimes they are aided by venture capitalists, investors looking to get in on a good idea early on and end up with a huge payoff later.