I filed my I-485 in Los Angeles back in September 1996 based on marriage to a US citizen.
The interview took place in December 1997. We brought a lot of evidence with us, and during the interview, I was not asked any questions at all! My wife, however, was asked one question - my father's name. That was it!
So, after waiting over an hour for a 10 minute interview, my passport was stamped.
I received my plastic card six weeks later, in January 1998.