Google: Taste Your Ass
The 2nd listing is "Your Lemon Squares Taste Like Ass - YouTube"
Two years ago you wouldn't have found a single 'mainstream' site on the top 10 pages in Google for a term like that. When that changes, and I expect it will change, those primary adult keyword domains will regain much of their value.
Hummingbird supposedly makes search contextual and is an attempt to future-proof google for voice search becoming more popular than text search. Someone will eventually figure out that mainstream searches for 'Lemon Squares' are usually things a person wants to say loud and clear into their phone, while "Gaping Pussy Fucked by Six Black Dudes" will continue to be the kind of thing many people prefer to text into a device rather than shout out loud at their handset. Voice and text searches yielding different results is likely on the horizon and adult search would benefit from that as well.
Most of all, when Google loses its strangle hold on search, the market will dictate once again how search should work... and there are still billions of people looking for Orgasms or Gay without wanting to get Wikipedia or the LGBT Anti Defamation League as the top results...
