So far, in the Appalachian Windmills game, ours have faded out somewhere around second base.
The sex moves have created one of the more interesting RP situations I've had in years, though: my Chopper is a eunuch, castrated in the violent gang raid that killed his family when he was a child. But we ran into a situation where the Brainer was trying to stop me from doing something but couldn't do so physically, and figured he might as well try to basically brain-fuck instead. He hit on a 10+, we had 'brain-sex', the Moves triggered, but we've established that you don't necessarily remember everything that happens in the maelstrom when you get out, so my Chopper doesn't remember it, only a weird impression. When he opened his brain next time, the Brainer happened to be in the maelstrom too, so my Chopper, suddenly remembering the first time, demanded they do it again. Of course, when they emerge, he doesn't remember why seeing the Brainer makes him feel all weird, and the Brainer player has been happily taking shameless advantage of it.
It's definitely opened up singular RP possibilities that probably would never have occurred to us if the sex moves weren't there to nudge the players to think about that aspect of their relationships, and because it's all weird psychic sex, the idea that it may look and feel completely different to the two PCs means that a vague description actually works better than if we tried to nail down the details.
-JC