Immediately after buying the car my wife drove it 3 hours to beach in the dark. She said the headlights were horrible (I must have put upgraded bulbs in the old Civic at some point). Since we are planning on having the car for at least a few years, and I've always wanted to do a projector retrofit, I jumped on the internet and bought a Morimoto mini H1 HID retrofit kit, some new housings, and LED bulbs for the front parking lights.
I'm hoping that 40W less draw (maybe a little more counting the LED parking lights) on the battery when the lights are on will help eek out a little bit more gas mileage. I'd like to replace most or all of the other bulbs with LEDs too sometime soon.
So far I've been really impressed by the light output.