Well, in the books, Deb has known since the end of the FIRST book, and lets it slide as Dexter is sort of a personal "get rid of the really bad guys" crusader, and LaGuerta has been dead since that book's end.
Maybe this season will end with THAT development.
Wouldn't say that I'd miss LaGuerta.
Deb knows in the books? I skipped the first one, but I don't remember any mention of it in subsequent books. I guess I'm going to have to go back and read that one. I was under the impression that the first season of the show followed the first book closely, then kind of went in another direction after that.