From Passport Stamping and applying for the Green Card, the period varies from Center to Center and from City to City within each center.
I think Atlanta, GA is the fastest for getting the actual cards. My stamping was done on Feb 25, 2004 and I received the card on March 8, 2004, so that was within 2 weeks which I think is around the fastest processing time. I have seen other postings where it has taken around 6 - 8 weeks and more also, so you have to go by the City/Center which you are in to really figure out how long it takes.