Nobody said they stopped. The article argues that the practise has become infinitely less effective, and Google is optimizing for their customers as opposed to their users.

For many queries, it seems the top result is just Stackoverflow, Wikipedia or something simliar, then a couple of organic links, and then just junk. And on the second or third page, the results just stop. I have a feeling that at this point, it is a mixture of white- and blacklisting, and single-page classifiers based on heuristics or "AI". PageRank is surely in there, but probably not dominant. (Sidenote: I wonder if they secretly do ignore rel="nofollow" because so many links use it.)

Funnily, I've used PageRank for some smaller search projects, and it still works very well if you use it in a vertical, say "educational resources" or "programming" or simliar. I just did a broad crawl, 3-4 steps from some known "good" seed URLs away, calculate PageRank and mix it in with Solr's classifiers.

I think you are right. They might be using a plethora of other factor as an addition to back links; however, genuine links from authoritative sources still seem to be the best "voting" mechanism to bubble up good content/results.

I can imagine that Reddit could join the search war - first, they have so much user gen content that people are deliberately looking for; second, they could use the voting mechanisms that are already in place to give preference to the "better" content. Of course, I might be wrong :).