I've just taken delivery of my first LED lightbulb (not counting my bike lights), and it's fantastic. It's a direct replacement for the standard halogen 50 watt spot (GU10 fitting) that everyone now seems to use in kitchens, bathrooms and even living areas.
Trouble with halogens is you put up half a dozen to light a room, and that's 300 watts! I've tried mini-flourescent equivalents, but the light is not as bright, and some of them can take ages to reach full brightness.
I heard that LEDs were now properly equivalent, so I thought I'd try one. I got mine from ebay - the seller I found does 5 for £35. That's cheaper than the best flourescents, and they last longer and cost less to run.
They're just 4.5 watts, so half a dozen of those add up to just 27 watts. And the amazing thing is they come on instantly and are immediately at full brightness. The light is truly as bright as a halogen. It's a very white light, so not necessarily what you want for a living space, but you can get less startling "warm" versions. And they are cool to the touch. Amazing. I'm sold.