It's huge in Japan, where Mixi.jp is the No. 1 social-networking site and the No. 2 site in general (after Yahoo), Forbes reports. But even Mixi's computer-based social networking is facing growing competition not so much from other Web social sites as from mobile-based social networking. "This year, for the first time, the number of mobile users accessing Mixi's browser-based mobile system outweighed the number of visitors who have PCs." And the phone socializers are younger than the computer-based ones, Forbes adds: "58% are under 25, compared with 43% of Mixi's PC users." Mixi's mobile competition is "Mobage-town," (Japanese shorthand for "mobile gaming town"), which doesn't even have a presence on the Web. Mobage-town users "send their avatars through a series of games, linking up with friends and competing for bragging rights. The free service has its own currency and pages where users can buy various gewgaws for their avatars." Forbes says the service claims "50% penetration among Japanese teens" and 8 million users.