After a week-long holiday in the Frankfurt-am-Main area, I find that I only managed to add a single point of interest to the map, one pedestrian subway, and add one tag to another point of interest, because pretty much everything else had been done in the area.

(Admittedly, I didn't go house number mapping, or out of my way to do any mapping)

I also worked out that GPS receivers don't work on the ICE3 trains (or Eurostar), and you can only get intermittent coverage on the S-Bahn trains in the area.