I think, in most ways, the average internet user doesn't understand (nor care) that the listing is sponsored. I could be wrong. I am going off my experience with friends and family who use the net. I try to explain that what I do on google and I am met time and again with "those are paid for?" remarks. If you look at some of google's (and overture's) partners, the distinction between what is regular and what is sponsored is VERY vauge. I think of all the SE, google is far better at pointing it out. Though, I am not quite sure that anyone notices.