Work of the author is supported by the Flemish Region in the framework of the BBT/EMIS project. The author is indebted to his colleagues at the BAT centre of Vito for their effort in writing the BAT reports that are mentioned in this paper;
for their enthusiasm;
suggestions and ideas: Anneliese Bernardon;
Geert De Meyer;
An Derden;
Diane Huybrechts;
Anne Jacobs;
Els Kenis;
Peter Meulepas;
Sofie Sannen;
Anja Vaesen;
Pieter Van den Steen;
Joeri Van Deynze;
Peter Vercaemst;
and An Vercalsteren;