|January 7th, 2012|
When you vote on one of these sites, currently, it only has a direct effect on what other people see. It's a very community minded act, which makes it not so surprising that very few people vote . If most of the time a reader responds to seeing something by voting it neither up or down, you're getting much less information than you could be. So perhaps apathetic voters would make this fail? If your votes directly affected what you would see in the future, however, you would probably vote more. Perhaps a lot more.
The main thing you give up with a system like this is that the site looks different to different users in a nonobvious way. Everyone who goes to Hacker News sees the same thing. Everyone who goes to Reddit sees the same thing except for the filtering of what subreddits they've subscribed to. This would be much more like Facebook in that I would need to expect my front page to look nothing like yours (unless we had similar interests).
I've found myself enjoying Reddit less over time: perhaps that's because when I started I had a lot in common with other users and their votes were a good predictor of my interests, in a way that's increasingly less true?
 The typical top story on Reddit has ~1500 upvotes (you can't get the total number of votes because the numbers they give are fake) and Reddit has somewhere around 2.5M monthly visitors. Assuming *everyone* visits every day, that's 83K people a day, of which only ~2.4% voted for the top story. The 'everyone visits daily' assumption is terrible, so the voting percentage is even lower, between 2.4% (everyone daily) and 0.08% (everyone monthly).
Update 2012-01-07: A friend points me to their 2008-2009 startup Newsbrane that tried to do exactly this:
Using an interface similar to that of Reddit, users vote up or down on stories. But instead of having those votes affect a global score, the site uses the votes to build an understanding of each person's tastes, and scores other stories for that user based on those tastes.