The reason why I ask is because I find it hard to actually make designs (or storyboards) for the behaviour of the site. Examples could this http://discover.store.sony.com/tablet/#intro or - even better - this: http://andrevv.com/
A really great alternative is to never design another parallax website again.
Amen to that!
In the past, I've used After Effects; just import your layered assets, turn them into 3D layers, add a camera, and start panning :) Unless you're taking that into something that supports 3D data, you'll probably have to recreate the parallax, but by then you have a good idea of the parallax motion.
I'd also love to hear what kind of other techniques designers have used.
Here is a super handy script for this - https://snipt.net/vmedium/parallax-scale-based-on-distance-to-camera/
Basically you move things back in z, and the script keeps the scale perfect, and even adjusts if you adjust the focal length of your camera.
Oooooohhhhh, good find!