Originally Posted by Tent Pitcher

From a link standpoint, I think it is almost the opposite...Adult sites are often buried in affiliate links, redirects, etc. - many of which can be completely irrelevant to a site's actual category. This can make it difficult for a search engine to determine a poorly designed site's actual content. There are also a LOT of adult sites out there and the signal to noise ratio is very high.

For SEO on an adult site, you just need to be extra careful that all of your efforts are as focused and targeted as possible. Don't go after the big-money keywords unless they are relevant to your site - it will only hurt you in the long run through penalties. If your site(s) are a mix of genres, it's oftentimes better to run a few targeted campaigns rather than a single generalized one. As someone else said, be aware of the popular spam keywords and phrases - like "penis enlargement" and "Cialis", and avoid them like the plague!

If you want to talk specifics, feel free to PM me.