We never could find those kiosks when we were in Animal Kingdom but then we didn't look to hard because the regular lines were pretty short that day anyway. At Hollywood Studios the kiosks by Toy Story would always be covered up so we would go use the ones by Tower of Terror. The lines were never really too bad, I don't think it ever took us more than 30 minutes and we were still able to get fastpasses for things like Star Tours and The Great Movie Ride. I could ride that one all day. Not so much Star Tours.
I have no idea where they are in Epcot, never saw them, but in Magic Kingdom we found some by accident near the bathrooms. So we were able to kill two birds with one stone so to speak and those lines usually weren't very long either, maybe 20 minutes but sometimes we'd get thru them faster because people would get in the line thinking it was a line for the restrooms and then realize it wasn't so we'd move up several places.