How to get people to look at online ads carefully

Take a look at Listen Game, a human computation game in the style of the ESP Game. From the Listen Game site:

Listen is a game that lets you tell others what you think about music. It also lets you hear what other people think about music.
Music is a subjective form of art. We all have our own unique experince when listening to a song. Even though you might think that "Hangin' Tough" by New Kids on the Block is "explosive and revolutionary", your friend may think it's "cheesy and annoying". Play Listen Game and see if the world agrees with you!

Now clearly, this idea can be used to give first impressions on all sorts of things -- not just music. And so why not apply it to online advertising? Not only would this motivate people to look at ads very carefully, but it would also give advertisers meaningful feedback on their ads so that they can improve them.