There is a 15{ish} page document that has all the lawyer written rules.
But basically, he needs to have, in his possesion, copies of everyones birth certs and ID's to prove that any given person who posts a pic in the [adult] forum, is over 18 and who they say they are.. Plus have proof that everyone who visits the [adult] forum is at least 18. You wanna give him Your credit card info and pay for it? LOL
OH, and some of the ad companies won't let you have adult stuff on your site either if you wish to be involved with them....

But thats the short version.