Maybe it's already known here, but I don't remember having seen it: The "Bundesministerium für Verkehr, Bau und Stadtentwicklung" (Federal Ministry of Transport, Building and Urban Development) in Germany published a guide (in german only) about the professional use of UAV: Nutzung von unbemannten Luftfahrtsystemen
It's a pretty clear guide under what conditions you need a license / authorization and how to obtain them. Most things are "good sense", which is pretty rare. In short: the guide clearly states as criteria the intended use: nothing particular to do in most cases of private and recreation use if UAV weight is below 5kg. Everything else requires authorization.