Shibuya-based Mobile web oriented HR agency Sapotant issued a research [J] on what social media buttons Japanese e-commerce websites are displaying to their customers (n=100).
48% of Japanese e-commerce site introduces one or more social media buttons. As shown on the chart, nearly 90% of who do, which is 42% of all, encourages users to tweet their site/products. Facebook Like and Mixi Check buttons follow. Which is not same as the situation in U.S., where Facebook leads and Google +1 is passing Twitter [pdf] (the research counts not only e-commerce websites though).
Link to full article