Planet13 - 4:16 pm on Jun 13, 2012 (gmt 0)
I haven't seen any evidence of this, either.
However, one thing I have seen - and this might be something purely coincidental but MIGHT actually cause an unintended legal issue - is that a lot of sites that are members of the Search Partners network (or that participate in Adsense) are ranking high.
One could see how google would benefit financially by giving preferred ranking to sites that generate income for google via search partners / adsense.
Again, no evidence this was intentional.