For my own entertainment, when the pay period switched to summer and the lovely full-time RA status (i.e., twice the paycheck), I started an Excel spreadsheet to track how much time I was really spending on work, with separate calculations for teaching, general student work, the specific projects I was working on. What I've found is that it's very difficult to actually spend 40 hours a week on my work.
This is a system that records the work I do in 3-minute chunks. It does not include the time I spend reading blogs online, chatting with other graduate students in the hall, or assorted other activities that frequently break up the work day of those on the standard 9 to 5 schedule. I had thought that this might account for only an hour's worth of time, in little bits and pieces over the course of a regular day. Yet even with my careful on-task-only, there is not yet a week with even 35 hours dedicated to graduate school work of any type.
It could be that I'm just more interested in spending some time in the sunshine than in getting more work done. It could be that, as much as I love reading, there are very finite limits in the number of journal articles one can focus on in a single day. It could be that the 8-hour workday is design to really only get 5 or 6 hours of productive work (which is what I usually manage). I might just take the delusional road and declare this last to be the case; spending 40 hours a week in the office just translates into 30 hours of time spent on task.
Meanwhile, only a third of my time is being spent specifically on the project for which I am funded this term. Throw in the basic "student" time (dealing with the never-ending emails, etc) and general lab time, and it gets up toward 60%. This was the real purpose of the spreadsheet; I'm not neglecting the project. I'm just neglecting comps and data collection.