More about Google’s supplemental index
I think I’ll make a category for posts about Google’s “supplemental index” as I seem to be a bit fixated on it. 
I was just meandering around the web and found this at Matt Cutts blog . It’s from Jan 2007, so it’s bang up to date, from the horse’s mouth info…
“As a reminder, supplemental results aren’t something to be afraid of; I’ve got pages from my site in the supplemental results, for example. 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. If you used to have pages in our main web index and now they’re in the supplemental results, a good hypothesis is that we might not be counting links to your pages with the same weight as we have in the past. The approach I’d recommend in that case is to use solid white-hat SEO to get high-quality links (e.g. editorially given by other sites on the basis of merit).”
