I consider it work time - i would not be away from my family and friends if it were not for this travel for work. My company tries to consider it my personal time and make us still work (bill) 40 hours a week. If there is work to be done that can be performed on the plane then i do it however we normally have to connect to servers to be able to perform our work so usually i am watching something or listening to music.
This is an ongoing battle at the moment.
E