Tracking Scroll Depth with jQuery and Google Analytics (opens in new tab)

All engagement metrics are pretty loose. Scroll depth percentage doesn't tell the whole story but to the degree that scroll tracking is useful, I think percentage provides a simple, document-independent metric.

Btw, tracking scroll points for specific DOM elements is one of the plugin options, so for instance you could track the end of the .comments div as you mentioned.

Yes there are more exciting options. take a look at pagealizer reports http://www.pagealizer.com/?page=report&type=demo and alenty reports http://www.alenty.com/en/demo/display-ads

you could try using server side GA. which try to mimic the js script using php. this is the most fleshed out version I know http://code.google.com/p/php-ga/

For statistical purposes all the people with JS enabled should be enough; but just for the sake of the technical challenge: 1) Link position, if they clicked a link under the first 1000 pixels of the page they probably scrolled. 2) Something similar but more complex can be done with images on CSS hover effects (using the webserver access logs) BTW, using something similar to this together with the "media" attribute on LINK tags allows you to see witch CSS file they are using, and therefore screen resolution.

I think only one person said it was cool :) What is disturbing about it? Do you feel it's a privacy violation?

I haven't tested it with infinite scroll but essentially it'll be a race. If the user can scroll to the bottom of the page before infinite scroll is able to load new content, the 100% event will fire. Otherwise it'll just register the previous scroll event (75% or a specified DOM element).