I think most sex scenes are lousy, or transgressive for the sake of being transgressive, or idealized, and none of the three do much for me. Some of the famously smutty novels recently strike me as particularly bad examples of what I want from my smut--neither Kushiel's Dart or Laurell K. Hamilton worked for me, as they say, the first because the sex scenes were passionless and distanced, without emotion or conflict, and the second because they weren't necessary to the plot and often felt as shock value written for the sake of shock value.
Which is not to be read as a sweeping value judgment on either woman's work. They did not work for *me.* I know tremendous numbers of people for whom they *did* work.
And frankly, I've probably read enough fanfiction just poking around on my friends list to say that I don't think much of the sex scenes in most fanfic, either. Although there's two or three of you ladies and gentlemen who do write some pretty amazing stuff, and I apologize for not commenting more than I do--please take comfort in the fact that I almost never comment on my published friends' writing, either, unless I'm asked to beta.
That said, I'm pretty proud of *my* sex scenes (and there's a doozy in Hammered.) And I think there are some professional writers who can write bang-up sex scenes--I mentioned Anthony Burgess and ellen_kushner over in Sherwood's lj.
ellen_fremedon's comments on transgressiveness and squicking in writing making for dull writing are, however, aptly aimed, and well-taken. It falls into the category of writing down the bone and bleeding on the page--getting *into* the grit and horror and blood and fluids of the character's soul, and not backing off when things get bad. There's a torture scene in The Stratford Man that was hella hard to write for that reason, and a sex scene, too.
And to my mind, the lack of that sweat and blood is why I didn't like Kushiel's Dart. But then again, a lot of the fanfic I've read (and I haven't read all that much, but there ya go) suffers that problem too--idealization, of sex or characters, or manipulation of them into situations that should be disturbing (rape fic) but one gets the feeling the writer is leaning toward a rape fantasy and not exposing a painful reality. (Which--exposing painful reality--is something Elizabeth Moon does very well in The Deed of Paksennarion, in my humble.)
Well, idealization, and treating grown men and women like gassy teenagers, but that's another problem.
(And again, there's good fanfic. I'm generalizing about the bad stuff here. There's also profic that suffers all these sins.)
As far as I'm concerned, there are four things that a sex scene needs to be successful, and they're the same four things any scene needs to be successful:
1) It must have conflict. If there's no conflict--if it's not important how the sex happens, but only that the sex happens, fade to black.
2) It must have evolution: *something must change within the framework of the scene.*
3) It must be *necessary to the story.*
4) It must illustrate a character's development, or failure to develop.
Also, I've learned that as near as I can tell, there is *only one difference* in the way men read and women read--in general, not in specific: there are exceptions in both camps.
Men in general cannot read through a sex scene to find the story underneath, and women in general cannot read through a fight scene to find the story underneath.
That said, almost everybody likes smut. And stuff that blows up.
Sex scenes! Huzzah! Explosions! Huzzah! A pirate's life for me!