[minstrel]

http://www.mattcutts.com/blog/infras...-january-2007/

A complete software rewrite of the infrastructure for supplemental results launched in Summer o’ 2005, and the supplemental results continue to get fresher. Having urls in the supplemental results doesn’t mean that you have some sort of penalty at all; the main determinant of whether a url is in our main web index or in the supplemental index is PageRank.

http://www.mattcutts.com/blog/google-hell/

this post from January includes a pretty good rebuttal of the “you get into supplemental results for spamming or duplicate content