tedster - 11:11 am on Sep 20, 2012 (gmt 0)
They use the data to improve the algo. But Google says the raters are not used to directly change the rankings.
Matt Cutts talked about this area informally at Pubcon Vegas last year - during an intense and extended discussion during the evening networking event. He described Google's use of human raters as algorithm testers - just as Sabrina described and He explained why only that use of human raters made sense for the way they build search rankings.
That's the only "confirmation" that I'm aware of, and it was definitely not a formal one, but it was very public. You know the way that Matt can get surrounded by people at conferences. I'm sure at least 20 people were in that group discussion, maybe 30.