[jQuery] How to monitor scrolling of a page?

Hey,

I am investigating to see if its possible to track how far down the
user scrolls on a page.

Ideal situation is track if they got to a percentage of the page
height like 90% or even if they reached the bottom of the page.

The intention is to integrate it into Google Analytics so that I can
save content engagement statistics.

Normally I would do this research myself but I cant seem to cut
through the noise in the search engines. It all seems to be code to
either have a scroll box in your page or scroll the user down to a
certain element. So I am turning to the jQuery experts in the hopes
that somebody knows.