Out of curiosity, where do you see the future of ads going as free ad-driven services, such as Facebook, start to approach market saturation?

Increasing revenue further would mean that product would need to increase ads, or somehow increase ad efficiency, but either case seems likely to deteriorate the user experience which could end up counter productive for all involved, at least in the long run.

I'm certainly oversimplifying things, but it seems like ad driven models have a very clear ceiling. Or is the endgame to simply to continue increasing costs to advertisers?