Banners, text links and all of the marketing tools you can use are good if you use them in the right way, banners are a good way to take the visitors attention while they are reading an article or review on your sites. Using too many banners will make your site load slow and might saturate the visitors view making them leave your site.
A good example of a nice way to use banners is the header on this forum, they present us a 728 x 90 banner that it won’t interfere our reading and still send us the message they want us to receive.
Bottom line banners are an excellent tool if you use them right.