Other then tons of constant gaming? Well let's see
I'm big into technology. I'm also a beginner game programmer and designer. I read a lot, not especially just sci fi and fantasy. But many things such as biographies, history books, philosophy, fiction, musical, etc. I play guitar, I study pop culture, the history of games, watch lots of sci fi films (not especially TV. Not a big fan other then The Twilight Zone) I've been to some conventions, I think all that tied up with the fact that I play games a lot qualifies me as a nerd. Now all I need to seal the deal is to get into D&D :unsure:
Not to mention that I'm active on a RPG developer forum
Edit: Like Freddo said, I think I would qualify more so as a geek then nerd. Considering I have very good social skills.