It's interesting Fran commenting that Google/youtube is trying to be Facebook. Interesting timing that is, since just very recently ebay also made changes in their site that superficially seem like they want to be another Facebook. Switching the whole ebay 'search' paradigm to 'follows' and 'feed', and some stupid idea that people would want to tell each other what they are 'following' (searching for.)
It's such a retarded, nonsensical idea that there has to be some other motivation at work.
Now suddenly Youtube is doing the same thing. Hmmm....
There are probably multiple ways to interpret this.
On one hand it could be that advertisers have noticed that conventional ads are no longer working. For one thing we're getting wise to them, for another they are less relevant in a world of devolved content production (and consumption).
They have cottoned on to the fact that targeted content is much more effective and a recommendation which comes from someone you know carries exponentially more weight but to make that work and enrol us all as unwitting (and unpaid) channels for their wares they need to a) encourage everyone to organise their social networks online so they know who knows whom and to get as much information about everyone as possible so that they know what to target them with - including tracking as much of their online presence as possible.
This, as has been observed above, makes Google - which is now basically an ad agency in disguise - lots of money and the more effectively they do it the better for them.
Another, more paranoid, interpretation is that no-one is allowed an opinion of their own any more. We must follow sheep-like what everyone else "likes" and bleats about. Obviously this is softening everyone up for whoever wins the Google/Facebook/Twitter/ebay mudfight to finally complete the mass brainwashing of the world's population. War is Peace, freedom is slavery and the chocolate ration has been increased three times this month already.
I suspect the first is closer to the truth than the second but I don't blame anyone who leans towards the latter.