If it is with a resistor, wouldn't it use the same amount of power as a normal bulb? I'm looking into LED's myself, but i can't find any H4 LEDs that are good enough (or legal, for that matter). I have found lots of P21 LEDs, but the powersaving over the standard 5w bulb is minimal, and not really worth the extra cost.
I did find these though :
LED autoprer - LED H7 Nr/Fjern lys 5500K (the website is in danish, but the H7 LEDs are korean made, but i haven't found them anywhere else on the web)
24W vs 55-60W for the normal bulbs and 1650 Lumen is a lot!
Edit: Just found them on a US site here
http://hidconcept.com/index.php?l=product_detail&p=119