I thought I might be in trouble when I arrived at 37 O St. NW in Washington, D.C. It was just an embattled-looking row house, yet the NeverLost computer in my Hertz rental car—which calculates the shortest route to your destination with the help of a Global Positioning System satellite—insisted I had reached Georgetown University, some three miles away. Computer navigation systems, it seems, are only as accurate as the humans who program them. Aside from the Georgetown mishap, however, the NeverLost (available in 16 cities on 8,000 of Hertz's midsize, full-size, premium, and luxury cars) performed admirably, no small feat when you consider Washington's numerous circles and diagonals. Is it worth an extra $6 per day?For those who can finesse a few buttons and don't mind being guided by a computer voice, it sure beats fumbling with a map.