Maybe everyone is being a bit judgmental here and missing a vital point. Porn isn't illegal and Google will judge sites like that based on the quality of the service and content etc just like any other site. The only issue is whether or not the referring site's content is relevant to the content of the site receiving the referrals which it clearly isn't and that could hurt the serp pos. The fact that it's porn is neither here nor there.
you shouldn't get punished by Google for those sites linking to you, because you really have no control of who links to you and who doesn't. Just be careful who you link to...
Certain forms of P. are illegal. Regardless of legality, I don't want to be associated with this. Its that simple. Has nothing to do with them being legal or not.