As humans, we make progress on monotonous tasks in an uneven way. When we start out, we're full of energy and tend to make quick progress. In the middle, we're tired of it and there seems to be no end in sight, so we go more slowly. Near the end, we speed up again because we're getting closer and we just want to finish.
Computers, of course, are not like that. They make progress evenly, and so they should. Perhaps, however, we should scale progress indicator bars to allow for that fast-slow-fast pattern and make it look more natural to people. For the first parts of the task, mark off sections of the progress bar quickly, then slow down in the middle, then speed it up again at the end. I'd like to do some testing to see whether this affects people's perception of the speed of the task. It might actually turn out to be better to reverse the process, going very slowly at the beginning when users have the high energy to allow for that, speed up in the middle to offset the user's lowered energy, and slow down again at the end.
Mokalus of Borg
PS - Some progress bars already seem to be fast in the middle and slow at the end.
PPS - So maybe someone already thought of this.