I remember the first A/S scene I read that I really liked (it also happened to be the first slash scene I really really liked). I was finding it pretty hot already, but then Spike whispered "Sire" and that was when I knew I'd never be the same again.

You using "Da" makes me a little wibbling puddle of goo. But when I see it elsewhere I usually kind just go eh? A very few authors can get away with it. You always can because well, you're you. You always write good talk-during-sex.