Many freelancers, including myself, calculate a man day as 8 hours of work. I've heard of stories that large companies count their work day as 6 productive hours for an individual programmer.
I know that other professions like a design or customer support can have 8 or 10 productive hours a day, but all programmers know what it means to achieve 6 productive hours a day (especially when coding nasty algorithm).
Is there anyone around who is close to some executive in an company to confirm how many productive hours they count as "one man day"?