How do I get the system to pick up my changes using Dropbox?

As soon as you save the files in the book folder, Dropbox will pick them up (assuming it is running) and the little Dropbox icon will look like a spinning thing. Once it's back to the green checkmark, Dropbox has the files. (Or, just wait about 10-20 seconds.) After this is true, clicking the publish button will trigger book generation with the latest files, since we always get the latest files from Dropbox.