Sleeping with your arm around a loved one—how sweet. Unfortunately, doing this in a conventional bed is massively uncomfortable. There is simply no place to put the extra arm—and its not like your loved one can just lay on it. If you do that, you might as well go the whole 9 and chop it off because it will be useless in the morning.
Fortunately, Mehdi Mojtabvi's Love Mattress offers a genius solution involving polyurethane-injected foam strips that allow arms and feet to fit snugly in the gaps. Apparently, the latter would be good for those who tend to sleep on their stomachs—but it doesn't take a vivid imagination to think of some other uses for that kind of traction. Too bad it is only a concept at this point. [Gooya Design via Freshome via Inventor Spot]