I have been mapping and digitizing professionally with ArcGIS for nearly 5 years. This is the first time I have heard of and used OpenStreetMap and it is awesome! So far I have made a few minor edits to the San Francsico State campus. I created and changed a few paths around the Library and Malcom X Plaza. I also added a few locations of handicap entrances and ramps. So far the only difficulties I have experienced is the limitations of the id edit tools. They are perfectly fine for the task of mapping points. For the paths, I found myself accidentally deleting entire paths. I was finally able to figure out how to split the paths and correct an area near the library. As I mentioned I have been mapping and digitizing using ArcMap for quiet sometime. The user interface using id is not much different. It all points, lines and polygons right! I am hoping to be able to add considerable content to both SFSU and areas near my place in Concord.