plc90210 - 4:21 pm on Oct 1, 2012 (gmt 0)
I had a near EMD where I just added an 's' at the end ([keyword phrase]s.org); I was certain it would lose rankings when I heard about the update. Before the update, it was ranking #5 for [keyword phrase] but after the update it is ranking #2. It had only 2 articles on it so the theory about # of pages being used to determine quality is B.S. The two articles were of high quality though and had backlinks from a few authority blogs in its niche.
I also had another near EMD ([keyword phrase]hq.org) that was ranking #8 for [keyword phrase]. It had a few irrelevant backlinks and a few paid backlinks that were relevant (the content was mediocre so I figured I might as well pay for links if I ever hope to rank this site). After the update, the site is nowhere to be found in the top 100.
Based on this experience, I'd say quality is determined by the same factors it always has been: BACKLINKS. Relevant links from authority sites are the best indicator of quality content and probably always will be.