South Korea leads the world in the popularity of social networking, with 55% of adult Internet users having visited at least one site, according to Ipsos Insight. Three out of every 10 Koreans belong to Cyworld, which markets itself as the Ultimate Place for Trusted Friendships and Creative Self-Expression. Ipsos found 27% of adults in urban China had visited social network sites, compared with 24% in the US, 16% in India and 9% in Japan. Another research firm, eMarketer, estimates that companies will spend $900 million in the US — and $330 million outside the US — on social network advertising this year. By 2011, it predicts those revenues will reach $2.5 billion in the US and $1.1 billion in the rest of the world. It expects lead players MySpace and Facebook will continue their strong performance but will face competition from hundreds of new social networking sites. eMarketer senior analyst Debra Aho Williamson says 2007 will determine whether a global social network strategy will make sense or whether home-grown sites will win out.