I moved a road. OpenStreetMap had one path for an obscure little road in Nevada City, CA called Woodwardia Place. I was curious about the exact path so I drove down it twice with a GPS logger, then used JOSM to upload a change. It’s cool how fast the upload took effect; the raster tiles for the map were generated anew within 30 seconds of my upload. JOSM is a bit confusing, and I never could figure out how to upload the GPX track for OSM’s records.
Here’s the edit; old road is in grey, new road is in yellow moved slightly north.
Finally I went to a different part of the map and removed a road segment. I’d driven blind down that road expecting it to go through, but the map was wrong. Never again! Removing a road segment is a bit tricky; I had to select the node on the western (non-existent) T intersection, “unglue it”, delete the incorrect line segments, then “merge nodes” to reglue the now-T intersection that does exist on the map.