I know that if I go to a site (any site, not just porn) I get annoyed if a console pops right off the bat & I tried to not go to those sites if I didn't have to.
Poping them when the surfer leaves - especially in porn - is probably a good use for them & since they were leaving anyway, why not try & get them to click on something.
Of course, now that I have a pop-up blocker that just notifies me when one tried to pop, I could care less
