Sara Donati -- whose books The Wife really enjoys, and whose blog I really enjoy although I forget about it for weeks at a time -- provides an interesting analysis of a sex scene from another author's novel.
I don't know if this makes me a prude or something, but I simply cannot write stuff like that, and when I encounter sequences like this in books in my own reading, I tend to gloss right by it. There's just something about the sexual act that is, to my mind, searingly private*, and in my own writing, when "the act" occurs, I generally avoid it entirely by leading up to it and then cutting to sometime after it. Sort of like the scene in When Harry Met Sally... when Harry and Sally finally make love: we see them kissing a bit, then more passionately, then we cut to afterwards (with the best cinematic juxtaposition of two entirely different facial expressions that I have ever seen).
I don't really have a point here except to note that I tend to approach eroticism from the standpoint of suggestion than from the standpoint of expression. That's just a matter of taste, though. The passage that Sara illuminates really is well-done, for the reasons Sara gives.
* Invariably, my most embarrassing work-place experiences involve moments when co-workers discover my general discomfort with this kind of thing and proceed to draw much pleasure from the fact that I blush incredibly easily.
UPDATE: Upon further inspection, Sara is spending some time over multiple posts, starting here, examining the forensics of the sex scene. I'll try to quell the voices of my inner Beavis and Butthead as I read her blog for a bit!