Mark Zuckerberg is visiting what could be Facebook's final frontier. His social networking site is banned in China but Zuckerberg himself was welcomed on a visit to the offices of Baidu, the country's leading—and heavily censored—search engine, AP reports. Baidu's communications director says rumors that Baidu is considering buying Facebook are "greatly exaggerated." Zuckerberg is traveling with his girlfriend and no apparent entourage. (More Facebook stories.)