What I have noticed is for competitive keywords only. We have a new site that is only 2 months old and it is ranking for almost all the none competitive keywords but has yet to show up in the serps for the primary ones.
I wonder if adwords and sandbox are one and the same. It would be easy to link the algo to the adwords. The more is spent, the more pronounced the affect. Forcing us to pay for display. I think I may be onto something here!!!!!!!!!!!!
I would have to agree with you to a certain degree. Its as sound of a theory as I have heard lately. To expand on it a little, I believe that the number of indexed pages also play a roll. Google is about money and the more difficult they make certain keywords the money chances they have of generating income through adwords.