Facebook, specifically, is struggling with the issue that strong correlation doesn't imply semantic value (i.e. posts with a lot of activity can be really good OR really bad) and corner cases. The semantic value issue they're addressing with the multifaceted "like" button.
The corner cases issue may not be fixed. As harsh as it is to say---and as unacceptable, perhaps, as it should be to work this way---there is a train of thought that goes "Even if we get the occasional bad result, when we have a billion users and 99% of the results are good; ship it. That's 990 million happy customers." The 1% bad results have to be really bad to tip the scales.
The corner cases issue may not be fixed. As harsh as it is to say---and as unacceptable, perhaps, as it should be to work this way---there is a train of thought that goes "Even if we get the occasional bad result, when we have a billion users and 99% of the results are good; ship it. That's 990 million happy customers." The 1% bad results have to be really bad to tip the scales.