I read the Hazel Chesterman Philips one which was appaullingly written, though the things she said made sense (but without a shred of scientific evidence, just lots of gushing testimonials). We tried to follow some of it though, but only for the first month. By the second we'd decided we didn't care enough, but we got what we were trying for anyway, after only two months of trying. I'm not sure if I would try it again as before having dd I was convinced I wanted a boy and a girl, but having had DD I no longer care and am happy to let fate decide.