I did my first serious batch of edits today. I installed both JOSM and Merkaater on my machine, and find myself more productive in Merkaater, so that's probably what I'll be sticking with. I've been filling in a lot of tertiary and secondary roads in West Seattle and Burien. Looking around at the standards used elsewhere in Seattle, it looks like some of the roads I marked as tertiary roads should probably be promoted to secondary roads, but I still need to hunt around.