I read about it its probably 60 to 40 60 in favor. One of the new machine comes with one. I would like to try one myself :D
here is one scroll down a bit http://images.google.com/imgres?imgurl=http://webstore.quiltropolis.net/stores_app/images/images_430/cmpf_fade.jpg&imgrefurl=http://webstore.quiltropolis.net/stores_app/Browse_dept_items.asp%3FStore_id%3D430%26Page_id%3 D17%26categ_id%3D1301%26parent_ids%3D0,1300&h=326&w=319&sz=41&hl=en&start=1&um=1&tbnid=XCSFRKbOVa0rAM:&tbnh=118&tbnw=115&prev=/images%3Fq%3Dsewing%2Bmachine%2Bfoot%2Bfor%2Bcurve s%26um%3D1%26hl%3Den%26safe%3Doff%26rlz%3D1T4SUNA_ enUS254US254%26sa%3DN