I was had the pleasure to work through the summer 0f 2002 when we tried using Carmen. It resulted in roster changes everyday because crew were constantly going out of hours. It rostered crew for a flight from different bases and you were constantly hopping off one a/c to get on another, and always started or ended your duty with positioning. When one a/c was delayed it had a knock on effect and by the end of the day the thing had snowballed and everything was delayed or cancelled.
Apparently this was not the fault of the software though. Our leaders in their wisdom decided to use the CAP371 max flight duty periods as the starting point for the software, so Carmen rostered flights right up to the maximum FDP, causing everyone to go out of hours. My duty one day was 17 hours, I couldn't even fly home in discretion because I had already exceeded the 3 hour extention to my FDP.
You wouldn't find anyone at easyJet who would have a good word to say about Carmen, but maybe it could be implemented better at other airlines.