The 'sa.yona.la' requires an OpenID authentication and the company logs all the activities with IP. Also, the Terms of Service explicitly prohibits users from abusing. In this sense, this service is far from an anonymous service like 2ch.net (do you know it?). That's why Japanese users love this service. This service is purely simple, and safe at least than many other anonymouse services. (Actually this service isn't categorized as an "anonymous service" in Japan.)