Dormcest is almost the opposite of incest, because while incest causes the most problems when the relationship goes "right" (leading to pregnacy and possible genetic defects
) dormcest causes the most trouble when the relationship goes wrong (and you have to see your ex regularly). The moral
of this story is: if you are going to date someone on your floor, hall, etc, make sure it will last.
When it does work it is convenient, as it is much less suspicious to appear on the hall at odd hours if you have your own bed. It also makes it possible to arrange your two rooms in a complimentary fashion (This works best if both people have singles, but at least it gives a choice of roommates/next door neighbors without needing to go outside.)
On my hall, there are several couples who have dated for over a year without any problems, but I haven't heard of any on hall casual relationships. Of course, the kitchens on our hall probably make the convenience of living near each other (and having the extra space for pots and pans) more attractive than in dorms that are only long rows of rooms.