When did you sign up for Facebook? If it was any time in the last 15 years -- the site launched in 2004, though it was very restrictive at the time -- then you probably saw the simple logo on the signup page. The page read "Sign Up" in large letters, and then had a small slogan below that read: "It's free and always will be." Always. It's something that many users have taken in stride. They expect that free content, that free ability to connect with friends, brands, businesses, co-workers and family members. In fact, a major part of the allure of Facebook is that it is free and anyone can use it. That's why it's the No. 1 social network in the world -- among other reasons. However, all of that could be about to change.