Nils, There are many practical applications of constraint techology. Of course, other fields in addition to AI, e.g. logic programming and operations research, have contributed to the technology, and the technology has found its widest commercial application when embedded in constraint programming languages and libraries. Example applications can be found at the web sites of companies involved in commercializing constraint technology. Scheduling is a natural domain for constraint technology. Monte Zweben talked about the commercialization of scheduling in his AAAI-98 Invited Talk.
Configuration is another one.
The current issue of IEEE Intelligent Systems is a special issue on configuration that Boi Faltings and I edited. Of course, you want to know to what extent they have gotten out of the laboratory. I'll circulate a call soliciting more specifics. We are also working on an AI Journal paper that presents the modeling aspect in detail. Below, I enclose a talk abstract to give a bit more overview.