Facebook.com, the No. 2 U.S. social network site that is quickly expanding beyond its college student base, has been met with <A HREF="http://www.publish.com/article2/0,1895,2013388,00.asp?kc=PBPWUEMNL090706EOAD">a sudden privacy backlash</A> by users after it made design changes this week. More than 500,000 of Facebook's 9.5 million members had signed an online petition calling for the company to back off a feature called "News Feed" that instantly notifies members when friends update their own sites.