I don’t believe in banners at all. Very often they are gaudy and “pushy”. I read an interesting article years ago from a power affiliate (I apologize, but I don’t remember who it was, and where it was published), but he said to stay far away from banners, and stick with text links (and meaningful content surrounding these text links). I don’t think there has ever been a meaningful study on the use of banners vs. text links, but I’ve always been a proponent of text links, for many years.