I periodically submit updates to various Wikipedia pages, usually around software process as that is my professional focus, particularly when I run into pages that could be fleshed out better.
I have a passion for 8-bit Atari computers and I am actively researching the history of the 8-bit Atari platform. I find these pages on Wikipedia to be really solid.
In my recent book Choose Your WoW! I used Wikipedia pages as references for a 100+ software development practices. In the book I asked people to get active in updating Wikipedia pages as many of them really could be expanded upon.