i've used it and i love it. i only used to buy with a 50% coupon, but now i just buy it as needed. it's great to work with, it's no more flammable than anything else (poly melts and sticks to your skin) and even though it has been treated with an equal amount of chemicals as anything else, it is a renewable resource. my daughter has a lot of allergies and this is comfortable for her. it washes very well. it's a little thinner than cotton, but just as warm. it's an effort now to use up the cotton batting that i have, and i can't always find the bamboo in king size.
it's lightweight and still warm, it's silky to use and any fluff cleans right up. i do not prewash my fabric or my batting - i let everything shrink together at the end. yes, it is 50 - 50 (bamboo) rayon and cotton.
http://isewblog.blogspot.com/2008/07/oh-bamboo.html
some info that may give you some more insight.