The German bureau of statistics (Destatis) has recently published a 669 page report on air transport in 2012.
Some interesting bits on page 10:
Starting page 550 some information on how different aircraft classes are represented at the airports:
Quite interesting stuff in there but some numbers are questionable because of how they get determined. Destatis sends questionnaires which you are required by law to answer truthfully but often their categories don't fit with your own databases (for example they don't differentiate between "airport" and "airfield" but they differentiate between commercial and non commercial which is not always easy to say for a smaller airport).
Non-commercial traffic from Heubach -98% because everyone is reading a German document in full :)
What are you doing??? It's a beautiful day, don't read, fly!
Aw, you completely underestimate my ability to draw (premature) conclusions from 669 page documents by scanning them for less than 2 minutes!
Also on Mondays, the restaurant at the airfield is closed