The problem is that search engine != video sharing site.
The sign of a good search engine is one where the user leaves quickly because the user finds the content they want quickly.
The sign of a good video sharing site is one where the user stays because the user keeps finding videos they want to watch.
So, in fact, I would find it perfectly acceptable if Google does measure YouTube's performance (and product quality) by a metric related to time spent on site.
The sign of a good search engine is one where the user leaves quickly because the user finds the content they want quickly.
The sign of a good video sharing site is one where the user stays because the user keeps finding videos they want to watch.
So, in fact, I would find it perfectly acceptable if Google does measure YouTube's performance (and product quality) by a metric related to time spent on site.