It doesn't work. According to published reports, the click through rate has plummeted to pathetic lows. If you ran some banner ads yourself, you probably saw similar results. Sites are even giving up on them altogether. The reason why the banner advertising medium is doing so poorly IS NOT because people have learned to tune them out.
Companies hire artists to produce their banner ads.
That is why their banner ads are not working. They look great. But nobody clicks on them. And it is ruining companies. But it gets worse.