Not in the way of erotic roleplay - if there's an image we don't need, it's you average tabletop gaming nerd pretending to be a virginal Elven maiden... or his friend playing the ravishing Half-Orc Sex-Barbarian.
(Sex-Barbarian is a Prestige Class. Requirements: BAB+3, Weapon Focus: Genitals, and the Rapey Demeanour Feat.)
But more like as a campaign theme - it could be a motivation, a plot point, or even just an overarching theme. Everyone (well, almost everyone) does it, so why ignore it? And in a fantasy setting, well, the sky's the limit for the weird and wonderful...
Or even the mundane. People have attempted birth control for centuries - from the Egyptians using crocodile dung pessaries, to the first sheep-intestine condoms, all are appropriate in a fantasy setting. Even other fantasy (but still non-magical) things like certain teas and herbs (Pathfinder even has Gentleman's Snuff - not only a quality idea, but a bona-fide male contraceptive!) could be used (and Gentleman's Snuff is totally getting stolen!).
And there are records of sex toys being made as far back as 2,500 years ago (those randy bloody Egyptians again). Just imagine the looks on your players face when they recover an ancient, amazingly well-crafted piece of art from a dragon's treasure hoard, only to find out it's a dildo? Materials like lacquered wood, stone, and glass have all been seen, and I imagine in a fantasy setting, the easy availability of things like gold, silver, and more unusual materials like jade, obsidian, or maybe some thing like D&D's Ironwood (stop that sniggering!) would make perfect materials for the rich and powerful Sorceress who can't get laid!
(As a side note, most campaigns with dragons will already have sexuality as a theme - after all, the Half-Dragon template can be added to literally anything. And as most of them can polymorph themselves into other forms, dragons are some of the biggest shaggers in your campaign setting. Bear this in mind when making up their treasure hoards in future!)
When you add magic into the equation, things get... weird. From the obvious (a Million and One Uses For Mage Hand...) to the weird and icky - technically, a Bind Planar Ally makes them do most whatever you ask... but is it rape? I mean, using something like Dominate or Charm Person to make someone sleep with you? That's a horrendous act. So using a spell like Summon Monster to do the same should be just as bad, right? But what if you summon a Succubus? These sort of weird questions rarely come up in the games I play, but hey, you never know...
There's also one issue that pops up from mechanics, which has sadly stuck in my head: D&D3.5's Lichloved feat. It grants you certain bonuses, and is a requirement for some weird prestige classes... but it requires you to have sex with an undead creature. Now, Vampires are technically undead, and that could be worse, but a Lich? Zombie? Ghoul? The possibilities are (sadly) endless. And exactly how do you present this to a DM?
"Yeah, I found this feat, it gives me what I need for my prestige class prerequisites. So, I go down to the graveyard..."
Of course, the problems of player maturity will always raise their head - after all, most people game for laughs, not for an in-depth look at the sociopolitics of sexuality in the Middle Ages. But, with just a few sprinkles here and there, one can add a layer of vermilisitude to your campaign by adding sexuality as a theme.
So I'm digging out an idea I had for an old campaign. Selene is a Tiefling Sensate who runs a curiosity shop (and will continually correct you if you try to call it anything else - she sells curiosities and novelty items) in the Market Ward of Sigil. Here, a canny buyer can find nearly anything he wants to help with his marital needs - for the right price, of course.
She's a Sorceress, who specialises in illusions - she can grant you a night straight from your deepest, darkest fantasies, for the price of material components and time and labour. From the simplest visual illusions (she is known to have the "cheap seats", where she projects images to large groups for a much reduced fee - perfect for stag-dos and Lad's Nights Out), to full-sensory experiences (let's just say she's really good with that Unseen Servant/Mage Hand combo...), she is more than willing to provide such a service to the wide and varied clientele of The Cage.
She also sells more "mundane" solutions - from Cold Iron/Silver sex toys, for the masochistic Fiend, to finely-crafted whips from the Drow (highly spun Phase-spider silk). If she can collect it from the Planes and find a... use for it, it's in the shop.
Selene frequently interacts with adventurers of all stripes - whether they are receiving or providing her business. After all, she has to run the shop, so someone has to go collect these oddities from all across the Great Ring. A few sample adventures...
- One of her regular clientele, Boagris (Bauriar Sensate Barbarian) has a very specific request for her - to be whipped with Razorvine while a Halfling watches. Razorvine is so common as to be a pest around Sigil - but how the hell are you going to transport a plant so sharp it'll cut through any bag you try and put it in? And exactly where are you going to find a willing Halfling?
- A shipment of unusual woodcuts is coming to Sigil from a Prime world, but the Guvnors are interested in keeping them out. Will you use stealth, diplomacy and cunning to smuggle the goods through, or simply batter hell out of the Hardheads till you can get through?
- One of Selene's rivals is taking things a step too far - they are using Planar Binding spells to take creatures from other layers of existance for their own nefarious purposes. She wants you to put a stop to it - if she goes herself, the Hardheads will be very interested in investigating her shop...
- As a follow on to the last adventure, when they break the Summoning Sex ring, they find a much darker side - kindnapping Primes to be sold off into slavery to the rich and powerful perverts of the Planes. Now, it's time to get the Law on your side.