Late last month, as part of a rare work-vacation trip to Asia, Mark Zuckerberg made a quick stop in Tokyo to announce the launch of Facebook Japan.

Facebook, a social-networking Web site that the 24-year-old new billionaire created while he was a Harvard undergraduate, is one of the most popular online communities in the world. But as Zuckerberg stood on stage at the Aoyama Diamond Hall convention center in his boyish red hair and black blazer, the audience was skeptical.

Facebook's entry into the Japanese market is definitely buzzworthy. But like all Silicon Valley exports to Japan, the site faces the challenge of penetrating the highly nonporous surface of the Web 2.0 industry here. Its success will depend largely on how it fares against social-networking site Mixi and its ability to expand despite its lack of localization efforts.