A controller at the Nashville, Tennessee airport told me about an incident from several years ago when he cleared a Cessna 172 for landing. As the Cessna turned to final approach, an airliner called in 'over the marker' (5 miles from the airport). The Cessna was about a half mile from the runway, and the controller knew he could land and clear the runway well before the airliner would land, so he cleared the airliner to land as well. A few seconds later, the Cessna pilot asked the controller, "How far behind me is that 737?" Before the controller could respond, the airline pilot keyed his mike, and in a deep bass voice said, "Don't look back!..."