LEDs have been introduced on traffic lights here over the last couple of years ("here" for me meaning the city about 20 miles away -- I'm too far out in the sticks to have traffic lights nearby!). They really get your attention because of the quick "snap" from one light to another. As yet I haven't noticed any suffering from problems, although the climate here is much milder for both extremes of temperature than most parts of the U.S.
Some late-model cars here are using LED lights as well. The center-mount high-level brake light is the most common candidate for them, but I've seen a few using them for other lights as well. They seem to be hybrid arrangements though; I've followed at least a couple of vehicles with amber LED turn signals on the rear but still with conventional filament lamps for tail/brake lights.
