maybe this and some other nice ideas could be implemented as some "predefined standard events" whose tracking could be activated within the backend?

I would LOVE to see this. We looked at implementing it as a custom page variable - but those need to be set before trackPageView() - so that doesn't work. Any thoughts on how to attach this data to page views? We'd be happy to write a plugin - just need to know where to start, or even if it's possible without a change in core.

@cemdev Maybe you could track an Event instead of using Custom Variables? http://piwik.org/docs/event-tracking/

it looks like events are session scoped, not page scoped, so to do that I'd need to come up with a way to map events back to pages. I don't see how to easily do that (maybe i'm missing something?). How would I map a scroll event back to the page that was being scrolled on? I suppose I could try page url or page title matching - but that seems pretty fragile.

+1 for this important feature to be added. e.g. http://www.searchenginepeople.com/blog/16063-page-scroll-depth-analytics.html

Note: this feature is part of Heatmap & Session recording premium plugin.

You will see a beautiful and useful Scroll Map report:

Scroll heatmaps use colors to visualize how far down in a page your visitors scroll. When you hover on the Scroll heatmap, you see exactly how many percent have scrolled down to a certain position. This lets you for example find out if there is important content positioned too far down the page, whether your visitors are encouraged to scroll, and more.

See other benefits of Heatmaps in the user guide: https://piwik.org/docs/heatmaps/