I will second this in the social sciences, I went to a top rated public liberal arts school and I studied at most an average of probably 1 - 2 hours per class per week. So that's 5 hours per week for a typical semester.
on my literature course, in the finaly year, more than once somebody read a 'presentation' that was copied straight from wikipedia, indicating they couldn't even put in more than 5 mins effort when they had an actual assignment. add to this that the majority of people never say a fucking thing in seminars, and the 5 hour per week figure sounds about right.