Lately, I've been hearing Google representatives using a new term - or at least new to me. Signals of Quality has been mentioned several times lately. One stage of the latest Bourbon update, for example, was described as "bringing in new signals of quality". I also heard the phrase a couple of times at the WMW conference.
So, what does this phrase, signals of quality, mean to us as SEOs? My guess is that Google is now starting to concentrate on a different kind of filter, if that term could be applied here. Rather than a filter that penalizes for some wrong-doing, these "signals of quality" are used to boost a site's ranking. I'm guessing again, when I say that these signals of quality may be coming from the patent application that Randfish summarized nicely here.
Things such as domain age, freshness, good prior rankings, etc. might all contribute to signals of quality for a site. It might be time to read through the patent application again, and see what we can do to make sure our sites have as many signals of quality as we can control.