My main task on Wikipedia is being a Recent Changes Patroller, which is basically detection and removal of vandalism, for which I use Huggle. I try to go about my work quietly (I don't need recognition, just co-operation!), but will occasionally kick up a fuss if things aren't being fixed properly. I also fix minor errors in articles I come across, and contribute the odd article or two (usually computer or computer game related). As so far, I have created two proper articles (X-COM: Interceptor and X-COM: Enforcer), and a couple of stub articles as well. I also try to help out with GAC elimination drives and do the occasional GAN review outside of this.
People ask "why do you bother?" on the whole anti-vandal front. It's actually quite a simple reason - it's actually quite funny seeing what people have done. Some people are actually quite witty and inventive and otherwise I'm easily amused. But at the same time, that's what a comedy club is for isn't it?