Using that metric has its own downsides though, depending on the content. If I am searching for some particular piece of information, the best site is the one

Using that metric has its own downsides though, depending on the content. If I am searching for some particular piece of information, the best site is the one that has that up front, which means I get in and leave pretty fast. Assuming that a user spending more time on a site is a good thing leads to large amounts of fluff (like with recipes...). But then again, there are some sites where that metric would be helpful.