We would like to express our sincere appreciation to all those who have contributed, directly or indirectly, to this work in form of technical or other support. In particular we would like to thank Markus D?chting for his assistance. A special thank to Lennart Gr?tzbach always helping us to find the right words. We would like to thank Thomas Geis and Jan Gulliksen for the fruitful and intensive discussions and the helpful input. We also like to thank the remaining interview partners for their help and efforts.