The top 10% contributors to these sites really do spend a lot of time and effort scouring the web, submitting reasonably high-quality content.

Most of these sites have anti-gaming measures in place.

Regarding your analogy … there’s a reason why Consumer Reports doesn’t sell ads in its print publication, and buys all the products retail that it reviews–sure, they’re losing out on revenue opportunity (selling ads) and increasing their costs (buying product vs. getting free review product)–it’s another measure to signal objectivity and maintain quality, which is why they still have an audience.

Once a social link sharing site becomes nothing more than a stream of random links by whoever bothers to submit one, it becomes unusable and will eventually die out. Sure, greedy opportunists can ride that until it ends by spamming these sites, but don’t ever think for a minute that “it’s okay” or “that’s what it’s there for.” Someone else worked hard to create that site and now you (whoever who is spamming it) are ruining it for the rest of us. You should feel ashamed.

If I discover content I want to access later, I’ll save it to del.icio.us. Or, if I think it’s something that others will like, I’ll submit it to StumbleUpon or Digg or Reddit or whichever niche site that the content is relevant to.

This system has worked so well that these social sharing sites have gotten as successful as they have. What I described is why they work–why they’re useful.

Now, the late adopters (i.e., marketing leeches) show up and spam them because, well, they can. There’s a reason why I don’t read Digg regularly any more. Newbies might think “hey, I have to promote my content somehow, right?” WRONG! Nobody needs to read your twaddle. You might want us to, but please don’t piss in the pool, for everyone else’s sake.

I always wonder though, is this also the chicken and the egg. If you don’t tell some folks, how will they even know if they like it?