I've noticed that it seems to be an art with persistence of vision. If you move it too fast, it may appear that the letters are in the wrong order. Moving it too slowly and you do not see anything other than the leds being illuminated.
Out of curiosity, what methods are you using to display your POVs? In the Tutorial, the photo is shown being wave, but also taken over a time elapsed photo, etc. Understood that this method isn't really meant to show the message, but as a means for testing,etc.
So, that being said, what methods are you guys using to calculate rotations, width needed for rotation for optimal display etc?