A lot. Well, personally I think that a majority of people not in graphics just like eye candy. So I think it does help a lot. However, I think people don't like clichéd stock images. Such as for a business you would have a picture of the team or something. They just look awful.
A lot, I mean if something is a page with words on it ( basic ) your not going to trust it as a professional business, or even think it good at whatever it does.
Where as if it is produce well, with nice layout and graphic content, the site appears to be professionally made, and as such you are more likely to trust the website that they can do what they say they can do.