I'm an experienced veteran of the internet industry currently living in New York City.
I've found Wikipedia extremely useful as a reference site, and contribute a littte time as a way to return the favor.
I'm enjoying deconstructing Wikipedia. I believe that it's one of the greatest web sites created so far. By allowing all to edit, it's much closer to Ted Nelson's conception of hypertext (which incorporated the idea of annotation) than the average web site. Wikipedia has been very successful in leveraging the small efforts of many (those who create the articles) to create a whole greater than the sum of its parts. I am a big proponent of open source technology, which Wikipedia brings the literate masses on a scale orders of magnitude greater than sourceforge. I also appreciate the similarity between Wikipedia and the guidebook in The Hitchhiker's Guide to the Galaxy.
Mostly I start articles on art, music, history, business, New York City, and technology--the topics that I know. I prefer to write short new articles than add to existing ones, as I am a rather slow writer. I enjoy planting seeds and watching the articles grow over time. The evolution of information and the convergence to a neutral point of view is great to watch.
The community aspects of Wikipedia are fascinating and worth study as a social phenomenon. There's several graduate thesis of material in there. I recommend The Professor and the Madman by Simon Winchester for all Wikipedians. It tells the story of how the Oxford English Dictionary was built primarily by a number of volunteers, including one who was institutionalized for insanity. A telling analogy for the creation of this endeavor. I had the opportunity of personally recommending this book to Jimmy Wales in 2005.
The majority of Wikipedians don't seem to be particularly good as graphic designers. If you don't know what you're doing, please stay away from the all the boxes and colors, and just keep things simple. Clarity is the goal.