My characters certainly do get it on, but I don't go into the nitty gritty details.
I don't want to read about who did what to whom and where did they put such and such, and how did they do it. And I figure most people don't want to read about these details either. Borrrrring. I don't want to know the technical details about my car either. I want to go out, turn the key and have it take me where I want to go.
Same with sex.
Dialogue can be very sexy. What characters are thinking about each other can be very sexy. Anatomy lessons, not so much.