People look for points of commonality with you. Where you came from. The school your kids go to. Whether you own cats or dogs. Even the pin you wear on your suit gives people an opportunity to find out what you do for fun on weekends. That invites conversation and relationship-building.
My wife and I just completed another Ironman competition (you can find our story by clicking on the marathon site at http://www.geocities.com/dhowlett2004/running.html)
And of course....I bought a pin!