You ever notice how the lot dots on the Kindle that indicate how big the work is are not really all that helpful? I think there are like 4 sizes, but all the little dots make you think there are more accurate. I loaded a bunch of short works from smashwords and some of them took like 5 minutes to read, and some like 30 minutes and they all show 4 or 5 dots....
I found the following on Amazon help, but it really just says they exist.
Kindle Books: Books are shown by title and author. Below the book title are a series of dots which give you an approximation of how long the book is. Bold dots within the series indicate how far along you are in the book based on the last page you viewed.