That's what this article in today's New York Times seems to suggest. That's not really a surprising assertion: I imagine many of us would react more harshly if we found out a significant other had cheated in a shared bed (or even in a shared apartment/house). What's a bit more surprising is just how much of a difference such an act can make for the future of the relationship:
In an informal, unscientific survey conducted at the request of The New York Times by the Web site CafeMom.com, which draws young married women, more than half of approximately 500 respondents said their marriages would “definitely not” survive if their partner made love to another person in the marriage bed. By contrast, less than a third of approximately 700 respondents to another question said that their marriages would “definitely not” survive an affair outside the home.
The Times gives a whole list of reasons why this act is seen as so heinous: it's an invasion of your territory; it's harder to dismiss as a fling; there might be children in the house. (It also gives a kind of gross list of reasons as to why someone might bring an extra-marital lover home: "hostility to the partner; a desire to be found out; it’s more discreet than a hotel; it’s convenient; it’s a decision made in a perfect storm of impulsivity, impunity and availability; home is where the nanny is.")
The divorce attorneys and couples counselors the paper interviewed claim that this kind of cheating is actually pretty rare: perhaps because it seems like such a slap in the face to the other partner, perhaps because people choose to keep such a harmful detail private. Or maybe it's because sometimes when the jilted spouse finds out, they light the bed on fire while you're still in it. Who can say?