The internet still hasn't figured out a way to profitably produce a high quality service or content with ads as the primary revenue source. So far, the only profitable approach is to reach the scale of Facebook/Google which would enable you to create your own ad network large enough to attract individual ad buyers. But, this does not mean that it's impossible or that we won't come up with a solution in the near future. And the people who I would bet on to create such a solution are those who are currently "working on ads".

It's a problem in desperate need of a solution simply because there are so many services (yelp, craigslist, pandora, etc.) that are free to users but expensive to build and maintain. It would be a shame to miss out on the next generation of ad supported content simply because we gave up on trying to make it profitable.