Amazon Best Books of the Month, January 2011: Yoga, even as it furthers its storefront-by-storefront takeover of American leisure hours, remains a punchline, a shorthand summing-up of a certain way of life. One of the charms of Poser, Claire Dederer's memoir of motherhood and marriage structured around her love affair with yoga, is that--as her title hints--she gets the joke, and tells it very well herself. She knows,...