When I attended my first DrupalCon in San Francisco I brought three suits. At that point, I had been speaking at (academic) conferences for a decade, and in my experience conferences were places where attendees dressed formally and speakers literally read their papers (here's a real example from a 2005 Women's and Gender Studies Conference where I spoke). I arrived in San Francisco thinking I would spend some time exploring the city while I was there, but I ended up spending nearly all of my extra time in the ChX Coder Lounge learning everything I could about Drupal from kind people in the Drupal community.