I can tell you, as someone in a long-term relationship, that these types of conversations are had more often than you would probably think. Still, their thoughts on murder are both pretty grisly, but I guess marriage will do that to you imagination.
Honestly, I haven't really been paying much attention to This Is 40 because I'm just kind of over Judd Apatow, but if this clip is any indication of the film as a whole, then I think I can find room for another of his flicks. I laughed out loud listening to Leslie Mann's Debbie describe how she would slowly cripple Paul Rudd's Paul with poison, lovingly take care of his frail body, then continue to poison him until death. Hilarious. The wood-chipper idea isn't half bad either, though, despite the mess. Who doesn't love a good film reference as a part of their murderous scheme?