I have the preview and I think the content of what is there is quite good if you are looking to add a more mature element into your game.
The section on alignments supplements the existing rules in that it shows how each alignment approaches relationships (and not sex) in general. While not every alignment has an example, the ones that do are well written and succeed in making you understand the thinking behind that alignment. For example, the Lawful Neutral section tells of how "the local noble has the option, nay, the duty, to initiate the newly wed into sexuality. It's a bond between the aristocracy and those who owe them fealty. It strengthens the bloodlines and makes the nobles care more about their people."
There is a very brief section on new uses for existing skills, four new feats and a variant rule adding Appearance as a seventh ability score (reminiscient of the 2nd ed. Comeliness).
The deities may not be everyone's cup of tea but are interesting. Vershnat is essentially a goblin fertility goddess while Kaladis is a deity that "formalizes the bonds of a union. He is unconcerned with love, passion, or other emotions-only the legal contract matters." Basically, marriage is a long-term commitment akin to an oath in his eyes and those who break it suffer harsh penalties. Each deity entry describes the behaviors of the clerics and has a dogma section describing the overall attitude of the deity and how it applies to campaigns. For instance, with Kaladis, arranging proper unions is crucial and many children are expected from that union so that the line may continue.
The prestige classes are primarily NPC in nature and do have some real game mechanics issues as indicated in an earlier post. The Vestigal Virgin really does not blend well with a paladin but rather should be an alternative paladin perhaps. The Disciple of Aaluran actually has some parallels in their overall attitude as worshippers of Sune do in FR. There is a more carefree attitude regarding sex and relationships. It does generate a ton of interesting adventure hooks and plot ideas for urban campaigns. The Dominator is definitely an NPC class in my opinion, and probably has what it takes to be a good add-on to an arch villain. I'd doubt I would let a player take the class because they gain some really powerful abilities like passing the pain and damge he sustains on to others. The Rake essentially uses sex appeal to get what she wants. It's more of an NPC class but I can see urban campaign rogues getting some use out of it. It's a powerful class, but the lack of strong sneak attack bonuses or the overall utility of her abilities acts as a balancing factor.
Magic and Spells gives us three new domains that fit with the overall theme of the book and several new spells. Most of the spells in the preview are sex-driven but have interesting effects. Block the Seed is the fantasy equivalent of a contraception. Fiendish Seed sets up the target to become pregnant and deliver a half-fiend child. Impotency is an overly powerful spell that permanents make one impotent plus a few other game effects. Kiss of Life is quite interesting, but I would make it bard only (as indicated in an earlier post about the mechanics issues). Mind to Mind is basically a telepathic communication spell. Reverse Gender has role-play potential written all over it. It does need to be a much higher level spell since it is permanent (Clr 2, Perversion 1, Sor/Wiz 3).
The Creatures section gives a few examples. The Fallen Cherub has tons of potential for storylines but would unlikely see much use. The Pleasure Golem is also more of a plot device. The Greater Succubus has, perhaps, the most utility of any of the creatures presented. MOre devastating than your typical succubus, this creature is not only a good plot device but also makes for good encounters for those cocky (no pun intended) adventurers.
Overall, the content in the book isn't bad despite the subject matter. Anthony has promoted the book to be more than just sex and that there is a lot of information on relationships and how they can be applied in game terms so I am interested in seeing the final product. The preview didn't have much regarding that, but then again, I didn't expect it would. Would I use the book in my world? Probably some of it based on what I've seen, but not heavily. Like any other d20 book, in all likelihood, I'll pick the parts I want and need and shelf the rest.
[EDIT: Spelling]
