I don't think LEDs are the answer to efficient lighting in a general sense by any means. LEDs have been around for forty years, as indicator lights. They can prove to be very reliable in small-scale applications, such as the power-on indicator on your stereo amplifier, or on your girlfriend's curling iron, to indicate when the thing is hot enough to burn her hair into the shape she desires. However, their efficacy, color temperature, and longevity (in line-voltage applications) consistently proves to leave MUCH to be desired, no matter how few watts they draw. (Not to mention how expensive their initial cost is for installation).
What I think is most important, in the interest of energy savings, is not creating lower-wattage, more efficient alternatives to the light sources that are supposedly "wasteful" (yet have been reliable for many years) but training people to understand what is wasteful and what is not, from a power-usage perspective. By this I mean, just because you have a CFL installed in your porch light doesn't mean you should leave it on all night because you are burning less power. Just because you are using CFLs in your home doesn't mean you shouldn't turn the light switch off when you leave a room. Unless you are expecting company at one o'clock in the morning, shut the porch light off. A room using incandescent lighting where the lights are turned off when unoccupied will always use less energy than a room lit with CFLs where the lights are left on all the time.
The major difference towards "traditional" technologies are thermal requirement - you need to lead away a lot of heat (order of input power), while still keeping the small (to keep their cost under control) chips relatively cold (<100degC to get reasonable life, compare to <200degC for HO fluorescents and ~1000degC for HID), what would limit their use to few watt's/fixture power levels, what is not much. Otherwise (on ~100W streetlight) there would be very heavy and large heatsink (so lantern) required.
