I actually was just watching that episode earlier and my only reaction was "Eww" oddly enough, haha. Not that I'm usually like that with sex scenes, they usually don't make me think anything one way or the other. Maybe it's just because I really dislike them together.
On a side note, the scene immediately after, with Xander and Anya on the floor made me go "Aww, aren't they adorable?!" (really, I said it out loud and I was alone o_o) so maybe I'm just biased towards my favorite couples and my opinion on this scene should be ignored...😀