I'm interested in urban planning and mass transit. As OSM matures further I'm hoping it will be a useful source of data for research. There aren't enough open data sets out there that people who aren't professionals have access to, especially in useful formats. I think OSM has the potential to change that.
One particular thing I would like to do is make maps of the San Francisco transit system. I think better ones could be made but at the moment all the data is locked up. To that end I've been concentrating a lot of my mapping activities on bus stops and bus routes.
I've tried to make the San Francisco page of the wiki a tool we can use to collaborate.
My mapping technique of choice is hand drawn maps. I walk down a street and mark all points of interest and their relation to the nearest cross streets and any other information. I then use JOSM to mark and tag all the points I've written down. I've used a GPS in the past and for this type of mapping it doesn't actually make things any easier because I still have to write down so much information. In addition to that in parts of the city with lots of tall buildings the GPS is less accurate. I also use walking papers some as well.
So thats me with respect to OSM. If you're in the San Francisco area and want to get together to map or grab a beer and talk mapping drop me a line or else check out our Bay Area OpenStreetMappers meetup.com page to see whats happening next.