Google says that advertising with them does not impact organic results, but I think it may, in the long term. I have a non commercial page that I started in 2002 in which I describe my personal diet experience http://www.jacobwissler.com/diet.htm
This page sells nothing, and promotes nothing commercial. It always did well on Yahoo and MSN, but Google always ignored it.
Then I put $150 into Adwords at 5 cents per click, and got zillions of people all over the world reading it (everyone wants to read about a free diet). My click through rate was 1.4. Now all of a sudden, the page appears in organic listings all over the place.
I suspect that Google noticed the traffic, and the fact that people were taking the time to read the page, and thus it started to show up in organics. Therefore, a small Adwords investment can improve organic listings?