Writing Sex Scenes

In the last two weeks I've read the following titles:

Take it Like a Vamp, Candace Havens
Short Steamy Sampler, K Matthew and Sky Corgan (Same author, I think)
One Fiery Night, Em Petrova
One Weekend Only, Christie Butler
Touched by a Demon, Ruby Winchester
Party Favors, Aubrey Watt
In the Barn, Selena Kitt
Connections, Selena Kitt
A Twisted Bard's Tale, Selena Kitt


My biggest question after digesting all that heat is this: How do they write these steamy sex scenes?

In my erotic writing, I plug along, easily getting my characters to take their clothes off, but choke when the real heat starts. Embarrassment, a frigid internal editor, I have no idea what's the problem. The transference from watching sex to writing it can be jarring, I know this.  To help me get over this hump, (punny, I know), I downloaded Be a Sex-Writing Strumpet by Stacia Kane. (I think she is also December Quinn?) A lot I already knew. As with any kind of fiction writing, a good sex scene should do the following:

1) Show something about the characters.
2) Show how the characters interact and the nature of their relationship.
3) Advance the  story
4*) Arouse the reader

Ok, #4* stumped me. Not all readers are alike. What arouses one, may turn off another.  This hiccup I recognized as the anxiety a lot of writer have over their audience. We want to please all of them but in doing so, we lose the story within us.  My solution, at least my solution right now, is to let the story flow naturally, uncover it as Stephen King says (On Writing) and until my characters achieve their happy ending (happy ending, get it?)