I was doing some agility and timing tests recently, trying to figure out my goblin clock, and ran into some data that contradicts what is popularly 'known' about DF.
Using runesmith, it's easy to make a goblin have any agility. So I was playing around with agility values. Naked, unwounded goblin, of course, although it'd be good to hear of any other variables people think might matter.
The first surprising thing is that a goblin with 1000 agility (the average) does not move every 10 frames. Most of the time, he moves every 11. Now, this would be easy to explain as an error by 1, except it's not even every 11 either: it's more like he moves every 10.9 frames. (In the pursuit of a 10-frame step, I settled on an agility of 1200: looks pretty good after a hundred steps or so).
For kicks, I looked at the same goblin with agility of 1 and with agility of 5000. The goblin with an agility of 1 moved every 14 frames-- didn't test for long enough to rule out fractions. The goblin with an agility of 5000 moved every 7 frames.
So I suspect that while 1000 agility is the typical value, it's not the value at which every thing comes out even. I'd suspect agility to function as a logarithmic scale, probably base 2, maybe natural log, but polling a few more data points could confirm it.