I fall primarily in the nerd/geek/gamer category so my default position is either in front of my computer or curled up reading somewhere. Don't mistake me for some kind of shut in though; eight or nine times out of ten if someone says 'Hey, let's hang out!' I am so there whether it's dinner and movie, drinks and dancing, board game night, I'm down for pretty much anything that gets me out of the house.
In social situations, I am usually the quiet one, listening patiently and just enjoying the company of the people I am with. In smaller groups, I might participate more actively in the conversation, but for the most part I stick with the occasional witty remark or observation and otherwise don't speak unless spoken too.
Finally, one last little tidbit for any MBTI buffs out there: I have taken the personality test and I got INTJ. If that last sentence made no sense to you, I would recommend Googling it. I don't live my life by it, but it is still rather neat.
I tend to use this site to people watch a lot. So if I looked at your profile but didn't message you, it probably wasn't because I saw something I didn't like.