[verycleanteeth]

It depends on where you start decreasing from. If you start at 0 and subtract 1 at a time you'll still follow Benford's Law. If you start at 999 and go down, you'll see a reverse curve that begins the process of righting itself again once it goes into the negatives.

[seasoup]

True, I was considering things like decreasing populations. Example, if you take all cities/countries on the planet with declining population and plot their current population, I would expect the reverse of Benford's law. Wish I had time to test this hypotheses :)