That's interesting.. Well I've been thinking of how well would they work along with a rich domain model and high level programming in general.. The book also has a chapter on systems of state machines, one of the suggested approaches was of an hierarchical model in which the lower stms input the higher ones only through their states.. Was the project you talked about embedded sw? BTW UML is also criticized by the book I mentioned, so hopefully it's not the UML trap again :P