My wife and I have an apartment. We're just starting out and struggling a little, plus we're trying, to save up for a house. So we decided about a year ago to have her friend move in with us. She needed a place and we figured we'd be able to save money on rent a little.
Anyway, her room is next to ours and the walls are thin. My wife and I are a little loud during sex and we kind of got a kick out of being heard anyway. Also, we have done it in places where we might get caught, having only been once so far, but it was worth it. Anyway, we were on the couch one night and my wife was on top and our roommate walked in on us. She looked a bit flushed and went to her room. Later that night, and many other nights since, we listened to see if it had an effect on her. It did. We heard her bed creaking and soft moans followed by 'uuhh, uuhh, ahhhh' that night and others as well. We've even heard her while in action ourselves, making sure she could hear when we climax. It has made for some pretty intense orgasms.