Funny, I was just reading a few good blog posts today on this specific subject, and it all depends, besides casinos I have a few other sites, and overall text links have better conversions, I get very few conversions from banners , but some can add character to a site if placed well, and people do click on them.
Whats more annoying to me is adsense , although not allowed on casino sites I do ignore it because you see so much of it.
But then again having a good article with a related small square banner does bring in some traffic.
Rod