Matt Cutts has posted a blog on the Official Google Blog indicating that google are working on improving it's search quality by removing content farms and 'low quality sites' from it's index, and using better webspam and compromised site detection methods.

This can only be a good thing for white hat SEO practioners, because the fewer spam sites there are in the results, the better the chances of non spam sites to get higher up in the rankings.

In the same post, Matt reiterates Googles official line on some commonly held misconceptions - ie, that displaying or paying for google ads have no effect whatsoever on the sites natural ranking. "These principles have always applied, but it’s important to affirm they still hold true" says Matt.