The ads, are what get dangerous. Many networks do little moderation, and I've seen malicious scripts used with them.
I'm saying this because I've already gone this route. Mainly as a piracy solution.
Anyway yeah there is still money to be made, but you need exponentially more traffic.
Deploying to the reputable portals that do adshare is feasible, but it's a lot of extra work, and there's a lot more competition.