JCE is right, LED lights will trip the bulb fault indicator on the dashboard.
LED lights throw light differently. They can't replace bulbs one-for-one. The whole taillamp assembly needs to be redesigned to take advantage of LED lighting.
We may see more and more of LED lights in the future. The biggest drawback for the manufacturer is cost. I'm surprised the DOT isn't pushing it. LED lights light up instantly, whereas regular tungsten bulbs need a fraction of a second to get hot and light up. All things being equal (braking, reaction time, etc.), this fraction of a second increases stopping distance of the car behind you by something like 10 feet at 60 mph. Ten feet is quite significant. Plus they don't burn out as quickly as tungsten bulbs. And auto designers can design thinner taillamp housings to increase trunk space.
95 E320 Cabriolet, 131K