according to some research, it says twitter has got 1% penetration and 12% awareness among the Internet users in Japan (article in Ja). Awesome, isn’t it? Without spending any advertising money ( I assume). But that article describes it quite negatively; making the comparison 40% awareness of mixi in 2004 before mixi broke with 12% of twitter today. The comparison is fair, but my feeling is that you just can not analyze the potential for the serivce like twitter in a traditional way. My feeling is that it has already tipped.