The only folks who really used stiff atlatl darts were/are the Inuit. At least that we know of.
This is an amazing link. Especially the first 50 pics. Incredible collection of ethnographic pics relating to semi-modern atlatl use by the Inuit, Mexicans, South American groups, Australians, New Guineans, etc etc.
http://users.skynet.be/fa057790/pictures/index.htm
For discussion, check out the World Atlatl Association section over on
http://paleoplanet69529.yuku.com/