If you've got something fairly unique or exclusive to advertise then you can't go wrong with The Hun. If you're trying to advertise some general themed Kara's or Cybererotica clone you probably won't make your money back.
On PPC search traffic you need to have a solid exit strategy to make money off of the non buyers. Its so damn expensive to get good keywords that its near impossible to get a good ROI otherwise.
Just my 1 and a half cents.
Good Luck
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Did somebody say Free Content?