Read Varian's paper (above), it anticipates a great deal, especially his commentary on Gresham's Law and content. There's also one from a couple of Stanford researchers a few years back which suggest a similar problem:

Currently, the predominant business model for commercial search engines is advertising. The goals of the advertising business model do not always correspond to providing quality search to users. For example, in our prototype search engine one of the top results for cellular phone is "The Effect of Cellular Phone Use Upon Driver Attention", a study which explains in great detail the distractions and risk associated with conversing on a cell phone while driving.... It is clear that a search engine which was taking money for showing cellular phone ads would have difficulty justifying the page that our system returned to its paying advertisers. For this type of reason and historical experience with other media [Bagdikian 83], we expect that advertising funded search engines will be inherently biased towards the advertisers and away from the needs of the consumers.

http://goo.gl/CTwEmw

Including in my tagging schemas for Pocket are quality indicators. I've been using an arbitrarily selected ranking scale of "a-1, a-2, ... a-5" to indicate quality (higher is better), and also tagging items with keywords indicating negative attributes (usually "bullshit", though others apply).

Being able to group classifications by reputation of author or publisher is also a key element. While there are hazards in argument from authority, there are frequently benefits both to recognising expertise and identifying non-credible or impeached sources. If a source routinely pursues some objective rather than the truth, you might tend to question its value.

PageRank essentially relies on the implicit reputation vetting of links, using link sources as a basis for quality assessment. It's useful but also limited. And as noted, the bias toward advertising and specific gain (see also Celine's 2nd Law, from Robert Anton Wilson's "Illuminatus" trilogy) raises issues.

I've been doing significant amounts of research, much of it online, but much also tracking down published book and article sources (most of those through illicit download sites -- really the only way the information can be obtained reasonably), and what I'm finding is that the noise associated with online data is just boggling.

Books, it turns out, compete exceptionally well with YouTube. Ultimately they compliment one another. Sometimes I want to read, sometimes I want a lecture or demo. Both have their place.

Excessive data ultimately isn't illuminating.

Yes, online search can be useful at finding out, say, what's happening right here, now (transit applications are a huge one), or within a given social circle, but both of those are domains in which an exclusion scope is set which rules out virtually all available results -- you're looking for information about a specific location and time, or concerning a specific group of people.

When it comes to general information, "reliable sources" dwindle. If you're looking for some established authority or text, you're left with the specific sources. If it's news, typically you're going to want some vetted news source -- and yes, that includes informally vetted sources on Twitter or YouTube. One of the most annoying things about both sources are the crap leaches who instantly show up to clog any trending keyword topic with crap content. That shit's got to get stomped hard.

For new and developing information, ways to broadly pre-filter and bubble up quality content are an interesting problem and one I'm actively working on. Community rather than broadcast methods strike me as more viable.