I'll generally throw in a moan or other noise here and there, but not excessively. The occasional "Mmm," or "Ohh," or "Ahh!" can help convey the experience, but it needs to be applied with restraint or it just gets silly. Something like "Ooooooohhhhhhhhhhhhhhhhhhhh..." is just overkill, and I think such exclamations are better dealt with descriptively (A long, low moan escaped her lips...)
Insofar as dirty talk, it really just depends on the characters and the situation. A scene with two innocent college roommates having their first lesbian experience would probably be more low-key in terms of purple language; on the other hand, a scene between some guy and a prostitute who hook up during his friend's bachelor party is probably going to have a little more "Fuck my cunt!" in it.
I find that most of the sex scenes that I write in CHYOA involve characters who are hooking up with each other for the first time, so it's natural that the dialogue be about what they each want the other to do; they don't have the experience to already know what their partner wants. It also tends to be in short, choppy phrases because I want it to sound realistic; as a rule, people don't make eloquent speeches while they're playing Hide the Salami. Finally, since my stories tend to be written in the second person, it's the "NPC" who gets almost all the lines while sex is going on, because it feels weird putting words in peoples' mouths during a sex scene. With regular dialogue, it's not as much of an issue, but for sex I find it flows better if the "you" character just doesn't speak.