A lot of us whose families have come over recently aren't able to trace our families back more than a couple of generations either. I'm only able to go back to my great-grandparents on either side, although I've heard that one of my uncles or someone has traced part of my family farther than that.
But I think that for a lot of families like mine, which is only second and third generation US, little is known about the families prior to emigration.