Originally Posted by RawAlex

Adult isn't as competitive as mainstream in many cases, but that has more to do with the limited earning potential in adult compared to many mainstream searches. With more and more "ad click" programs out there providing adtext style ads for sites, many people are making a good living off of building landing pages and stuffing them full of PPC ads. So there is huge competition on the mainstream side for that type of traffic.

Adult has burned a bunch of that already, and in most cases keyword buys through these systems aren't give the returns that programs need to make it worth doing, so the prices aren't as open ended. It is the reason why adult high traffic / low return sites are all over dating and stuff, because they feel this gets them the most money per click.