A few months ago I started a mapping project for the UK football (soccer) grounds/stadiums.
Well now I am over a third of the way through with 55+ done so far...
Confusingly I have started alphabetically by stadium and not by club from the list I had and some stadium have been renamed, built new ones, etc.
Most had some sort of reference on OSM already and had only found a few that were not mapped at all.
It is interesting to see the level of mapping in the UK as I have been up and down UK (via Bing). Some has fantastic levels of detail, others are sparse. But best of all is the changes, in just a couple months, to the areas that I have back to again where another stadium in the same area or to check details.