One of the great "watch ads for money" stories from the dotcom era was AllAdvantage. They were set to have a blockbuster IPO when Fortune magazine ran a story on them entitled "Meet the Dumbest Dotcom in the World," and that pretty much killed it.

This operation is still going - https://unlockd.com/products/unlockd-loyalty/

Once upon a time there was a Spedia with their browser plugin which tracked, IIRC, what ads you've seen and when. You had to see a new ad every 60 seconds otherwise you wouldn't get paid.

Here's an example but in Chinese: http://www.coohua.cn/