Unfortunately this script does not seem to work (visually it seems it does, but in the background it does not)
See the network tab here (cache disabled): Dropbox - lazy.mov - Simplify your life
All the images are loaded right away, also the same on the site you posted (goodbooks).
The problem is that images have the “src” attribute set, as long as this is set most browsers will start loading it right on the load.
@cskelly some working (but unfortunately not AS simple as this) solutions in this thread: Lazyload for Webflow Images - #15 by cheechee
@jordanphughes nice work on the goodbooks page! Funny to see the text hover underline effect (my site and brand logo: https://wave.si/ 
)