Originally Posted by bwit
That's right. No subfolders and no difference for Mac vs PC.
However, you may, if you wish, create subfolders of the documents folder (or audible folder) and put your files there and the Kindle will still find the files in those subfolders, index them, and let you read them. It won't show the subfolders in the home menu, they'll just be listed like any file.
Another neat trick you might want to do in advance is to put a stereo mp3 in the audible folder and it, too, will be listed in the home menu and playable. Maybe a recording of folks wishing your dad a Merry Christmas? [If you put it in the music folder, it will not be listed as pickable from the home menu, only playable as background music in shuffle mode].