Facebook's News Feed algorithm is getting a major kick in the pants as they're reportedly adjusting their algorithms to take into account how long something is visible on your screen or how long you hover over it. This makes a lot of sense in many ways because you're not necessarily going to like everything that you see on Facebook even if you do find it interesting or valuable in some way. For instance, if a volcano erupts in Montana and kills 1,000 people, you'd certainly find it newsworthy, but clicking Like on that post would feel very odd. Given that a dislike button is probably not happening anytime soon measuring social relevance and engagement from certain types of posts like this is made much more difficult.
Given Facebook's greater emphasis on people finding their daily news and using Facebook for things other than just social interaction, taking time into account seems like a very smart addition that should open the door up for other social signals and other factors for their EdgeRank Algorithm besides just obvious statistics such as likes. This also means that various social marketing agencies will need to focus their offerings on more of a targeted and relevant audience to better serve their customers. All in all, this is a pretty exciting development if it proceeds as envisioned.