I've been almost contributing to this project since it began. I've been mapping, writing code, organising events and generally been part of the community. If you've been to a State of the Map or a London pub meetup then you've probably met me!
I just started running the Engineering Working Group, I'm on the Vandalism Working Group and used to be on the License Working Group. I've contributed to the Rails Port and API 0.6, and wrote the Duplicate nodes map and the OWL system (direct link) it's built on. I helped out with some of the analysis for the 250 Cities project. I gave a talk at SotM10 titled OSM without Delay, which was about minutely diff updates and a bit about OWL.