Here is a recent article from the Japan Times Online detailing the rise of yoga into the fashion and culture of Japan, driven by women in their 20's and 30's. Compared to older versions of the trend, the new version of the trend is focused on more of the physical culture of yoga with "Hot Yoga" and "Power Yoga" being the trends of the day, driven by the demands for weight loss and a sleek body. Its seen as a new fashionable sport to lose weight.
Its interesting how the the celebrity culture of yoga is defining how it is seen. What has traditionally been more a spiritual approach to cultivation of the body and mind is now more widely known as a sport, which is not entirely accurate to the roots of yoga. The article doesn't really do justice to the full history and discipline of yoga.