I've never traced my family tree back very far, but I have talked to my grandparents a little about their parents and grandparents and have a copy of our family tree back that far. I did it as a school project many years ago.
My uncle spends a lot of time researching our family history and he travels all round the country visiting graveyards and cemeteries as well, to find long lost family members! He's uncovered several family secrets in the process, including an illegal marriage and some cousins with an extra finger on their right hand.... no, really!
My father's family is more of a mystery as there was a big falling out back in the 1940s and he and his mother lost touch with nearly all of their relations. Someone contacted him recently claiming to be a cousin but he decided not to follow it up, he's happy with the family he has.