Ads done right!
I have a major distaste for in-app ads. In most cases, if an application has ads built in and I like the app, I'll spring for the paid ad-free version. If there is no ad-free version, I'll usually get rid of it altogether. Most recently, I tried out God of Light and was initially put off by the 20s videos between each level completion. As the game rapidly grew on me, I decided to pay to remove the ads but there was a little twist that I've never seen used before.
After paying, watching the ads between levels weren't gone completely, but instead became an option. Why the hell would I opt to watch ads? Well, you're "rewarded" 2x fireflies or hints for each video you watch. So instead of ridiculously priced IAP's, I play a video which I never watch anyway as I divert my attention elsewhere for a few moments and I add to my hint pool.
I absolutely love this implementation and I think other developers should follow suit if they feel they need ads at all.