I don't go around telling people, and making a big deal of it. But I don't care too much if my friends know how geeky I am. The only people who've ever given me stick about my geekish tendencies are my brother and dad, and they just make fun of it in the same way they do everything else (although my brother genuinely seems to dislike that side of me, whereas my dad just jokes around like he does with everyone else about stuff).
But yeah, I won't specifically go out of my way to hide it or reveal it. If my friends know then that's fine, as long as they don't look down on me for it (but if they do that then they're hardly real friends anyway). My new flat-mate attends a film-making society with me at university, for example, and my former housemates know I'm into video games and stuff, and was interested in joining the university Assassin's Guild (though admittedly they did see that in itself as kind of odd...)...