Depends on the ad usually. As a general rule, an unobtrusive ad doesn't bother me. It doesn't actively sway my likelyhood on buying a good or service. But it doesn't make me NOT want to buy it either. Pop up ads, noisy ads, overly flashy ones, and hidden 'on click' event ads that bring you a pop up or to a new page alltogether for clicking anywhere on a page or even clicking on what normally would be a link to someplace you want to go but get hijacked by the code in a border ads js waiting for an onclick event to happen anywhere on the page... those ads make me angry, they aggrivate me and make me far less likely to want to support a product that can't be tasteful with their advertising. Same goes for the websites that don't moderate and keep control over their adspace. I'm less likely to visit those sites, and if I need to go there, far more likely to disable javascript and use adblockers to make the experience tolerable.