(Couldn’t find anything related on the forum)
I noticed extremely slow loading time measurements for some major commercial sites: 15+ secs. In practice, this is not what a user perceives, because 95% of this loading time is spent waiting for external ad servers, while the main content is loaded under 3 secs. For example, major Dutch newssite http://nu.nl loads its main content in under 1 sec but takes another 9 sec for many ad servers.
I’d propose a “perceived loading time” metric, that would block all requests to external domains (but would honor requests to subdomains though). In general, this would block non-essential content. Or perhaps this is possible already somehow?