Today I had someone email me about purchasing pop-unders for this site. I said no way, I am not going to do that to my users. But then I saw this thread at Cre8asite named Do adverts and pop-ups affect ranking?.
In the thread, someone asks the question, "do you think adverts can restrict a site ranking well from a search engine perspective?"
Ammon Jones answer "No."
But you see how careful he was with the question? He asked, before replying with an answer, do you mean "do they" or "can they". :)