You need the "enter" before the "exit" too many people click on the first link they see. Preferably have "exit"
below the "enter" link too.
I am guessing those who leave without looking at the porn are mostly people just hitting the wrong button by mistake. But where are you getting traffic from? If it is 'exchange' or 'paid for pops', a lot of people are probably being sent to your site who don't want to be there.
As to using link text for Google, that is a good idea but make the Enter a lot bigger than all the text. Also pick words that you might get a chance of getting listed on, those ones are too common, using them there may move you up from site 100,705 to 100,700 but what good is that?
Take a look at the enter/exit links on
http://www.wildjunglesex.com/free-po...-pussy-licking to see what I mean in both cases.