We tried a lot of stuff and it all comes with trade offs. When we forced the entire page into the gpu it made the things you mentioned (top/bottom, etc) a lot smoother, but it made other sections (notably CSS filters) much laggier.

The 3d parallax-y thing, or just all of the animation? After we got to a certain point we just figured to commit to it and go nuts!

Firstly, it wasn't a dramatic "omg I'm going to hurl" thing.

It was scrolling down the page pretty swiftly, basically skimming the site, and all the motion and movement caused me to feel a little "off".

Essentially the same thing for me I only made it half way down the page (but my eyes are tired and sleep deprived so that may not have helped).

I'm not sure where the concept came from, but it just seemed natural. The specific design was ours, but I'm sure somebody's done it before!

I'll take one too! This took me Skrollr and week solid.. And that was after all the photos and design was taken care of for me!