Okay, I downloaded it and finally read it.
First thing: it's hilarious.
Second thing: it's useful and can be deadly serious. I will fully recommend this book for adults who can successfully treat sex as natural and can enjoy it in their games. There are some classes I'd definitely use (the Tantrist and Kundala for instance). Why? because they gain the best benefit from sex: using sex to reach enlightenment or to boost creativity. Sadly, there isn't a Tantric healer class (imagist?). And the spells are sometimes useful to kinky to perversion based spells.
The book talks about sex in a matter of fact way, and treats sex as a serious, good subject. All of the pictures in it can be construed as pornography, or just erotic art in a good way (a couple is photographed having sex, and its beautiful, as all sex is beautiful before the Universe!).
but frankly, you need to judge your players before you use the adventure ideas in it. Some are light hearted (The Town Mayor has openly declared that he's gay!) to humorous (an ogre has fallen in love with our lord's daughter!) to Strike-me-through-the-heart serious (a gay paladin asks the adventurers to help reinstate him to his church).
But the book is useful. How you use it depends on your players and yourself.