Somewhere stupid I imagine. The boys being given to the Others wasn't even divulged until the next book as far as I can remember. This plot line just seems like such a far flung departure that it's questionable to the extreme.
Again, it's very different from the book, you can't venture into a character's mind like in the books, you have to show the audience if you want them to get into it (similar to Stannis and Mel getting it on).
Also, they may have also felt that Jon's plotline in ACoK was a bit slow and just added a bit of intrigue.
(that said, I agree with you, I personally don't like it as I don't see how they'll keep the Craster story in accordance with the general story in the book)
I'm starting to get annoyed with the sexposition stuff
Also, I'm not sold on the actor playing Stannis. I picture Stannis being this sour, emotionless rock, he doesn't quite seem to be getting there. Maybe the actor's having a hard time getting the character....