It was early in the new century, and some of my regular web-surfing stops were Zompist, Not My Desk and the Brunching Shuttlecocks. I'm pretty sure that I found Metafilter through at least two of those sites. I remember following the September 11 thread as it was happening, so I was a surfer in the fairly early days, although I didn't join until 2006.
Advice for Dads of daughters
Ten days after I joined, the famous Daddy-Daughter advice thread came along. My first child, a girl, was was barely four months old at the time, and since I came from a less-than-stellar family background, I'm always interested in anything that will help me relate to my own kids in a healthy way. It was that thread that solidified my feeling that MetaFilter was a community I wanted to be a part of, and one that could make a positive difference for me.
Thanatopsis had a comment in that thread that was the first one I favorited. When I'm having an especially good day with my daughter (now 5) or her two-year-old brother, or their new baby sister, I still think "You could have punched me straight in the face for the rest of the day, and I would have just smiled and said thank you."