Worrying about the effect of strong AI on sexual relationships is like worrying about the effect on US-Chinese trade patterns if the Moon crashes into the Earth.

Who says? I mean, computers can be used for multiple purposes, and although some applications of AI seem more "noble" or "intellectual" than others, the pursuit of knowledge and sexual relationships are both sense pleasures that we indulge in to make ourselves feel good. On a very large scale, one is hardly more noble than the other.

You're right. You should get in touch with the author of this http://lesswrong.com/lw/xu/failed_utopia_42/ and tell him :-).

...or like worrying about being on board of a heavier than air aircraft (surely that's impossible).

And yet, I feel that US-Chinese trade patterns could directly affect my life.

Maybe someone can hack a dating/popular fetish forum or one of the many IM services used heavily for that sort of thing and we can get a dataset to teach computers to sext!