Although I hadn't come up with anything more concrete than a feeling, Martin pointed out a specific way in which determinate progress is better than indeterminate: you can decide whether or not to pay the price of a mental context switch, do something else, and come back.
What's interesting when you're using it like that isn't the percentage complete: it's the rate of change. "It'll be finished in two seconds; I'll wait" versus "I've got time to get a drink and come back".
Odd that I hadn't noticed myself using it for that, but I do. At least with other applications; I'm quite patient with this particular application: I've got some half-formed thoughts in my head that want to be translated into check-in comment, and I don't want to get distracted and forget anything.
I think I mostly use determinate progress to work out how long I'm going to have to continue to wait. This belief seems to be borne out by the fact that I sit reading the text in web browser download windows rather than watching the progress bar. (Though I'm sure that subconsciously the continual motion towards the goal helps me endure the wait.)
I make my own determinate progress when reading a book. I've always thought time was the most useful unit. "How far is it?" "About ten minutes' walk." "How much more have you got to do?" "I'll be done in twenty minutes." So when I'm reading a book, I don't care how many pages are left; I care about how long it's going to take to read the rest. In particular, should I finish this book now, or should I put it aside, get some rest, and finish it tomorrow? Mostly I use the relative sizes of the "already read" and "still to read" page groups to judge the time. Other times, I'll find out how many pages are left and assume a constant reading rate. 30 pages/hour seems to work quite well for English.
Page numbering is an unusual reason I loved Chuck Palahniuk's "Survivor", and might have done even if it hadn't been probably his best book: it's the only book I own where the page numbers count down. Why aren't more books like this? Page numbers only increase because there was a time when this was the only convenient way to do it. If you were setting a book, you'd have to go forwards or you'd risk arriving at the end of your work (the beginning of the book) in an awkward place on the page.
You could argue that humans have a natural tendency to count up, but I'd argue that even that is the same kind of convenience. To count down, you need two fixed points; to count up, only one. This is why, unlike mathematicians, programmers tend to have the y-axis increase downwards, because it's easier to implement documents that grow if you don't have to recalculate everything's position every time you append something. Gap-buffer implementations in text editors also reflect the same fact: it's easier to expand something if there's space waiting to expand into; if only one point is fixed.
Anyway, there's no reason why a computer couldn't number pages backwards, in a separate pass if need be (TeX numbers citations in a separate pass). It's not as if one direction is better than the other for referring to material – which is the only other use I can think of for page numbers – page numbers are pretty weak compared to HTML anchors, and even they're weak in the face of modification to the document since the point at which the reference was made.
In the case of "Survivor", the page numbers are backwards because it's relevant to the story, which I won't explain here. Read it yourself.
Electronic texts are particularly poor at proving this kind of feedback, almost to the extent that I wonder if their developers think that it's not important to provide feedback for active activities such as reading; only passive ones such as waiting. There's certainly nothing to match the feel of a book in your hand, the different thickness touching your left and right thumbs. Continual subconscious feedback like that isn't easy to do on-screen, though an "all on one page" format seems like a good work-around. The vertical scroll bar divides "already read" and "still to read", and you at least have visual feedback about how far through you are that you otherwise lose.
And now it's time to put this aside, get some rest, and write some more tomorrow.