It is a shock when all of the sudden, for no reason, all my sites are becoming supplemental results (all pages). I have them all in different servers, different content, no links to each other... The only thing they have in commun is the Adsense code.
They are very white hat SEO and very clean. No reason to be punished!
From what I think I may, or may not understand from the G representatives, many pages that are in the supplemental index, are relegated there due to insufficient PR, and are not considered by G important enough to be in the main index.
I do not agree with this strategy, if this is indeed what they are doing.