I've been fixing small errors I see on my Garmin while biking. I did a little import of some USFS shape files in Oregon. See also my http://openstreetmap.org/user/Tom Brown/diary.
One of these days I'll write a tool to convert stops and shapes in a Google Transit Data Feed file into a osm. There are a few agencies that have published data but the licenses are often pretty restrictive so the agency may need to import their own data.