The utterly insane way the Danish community forbids linking addresses to POIs (shops, restaurants, you name it) comes to mind. They've built a system where they import all addresses, but they never managed to make it work in combination with user contributed data, so every address gets deleted unless imported by their official import tool. So a restaurant can never get associated with its address in Denmark on OpenStreetMap.

Meanwhile, the Dutch community also imports all official addresses, but there the tool simply allows for these to be used with other OpenStreetMap tags. It makes you wonder about the Danish approach.