SAN FRANCISCO - Facebook founder Mark Zuckerberg today unveiled major changes that are in store for the hundreds of millions of users of the social media site.Speaking at the annual F8 conference in San Francisco, Calif., Zuckerberg explained that at the heart of the newly redesigned Facebook is the Timeline profile, which will integrate all of users' online social history in addition to making it easier to discover friends' tastes in music, movies, books and apps.However, as Facebook began rolling out the changes to its front page yesterday, some users rejected the new look almost immediately.Many were upset that Facebook now has a ticker showing everything their friends are doing in real time. Also, some were unhappy with the way that Facebook now filters Top Stories to what it thinks is most interesting instead of a chronological list. Editor-in-Chief Lance Ulanoff says with these changes, 27-year-old Zuckerberg may be taking a gamble with Facebook's 800 million users, many of whom are not young people. "He's serving an audience that's probably in large part older than him, and isn't always as interested in what's new as opposed to what works," he says.