I've had one of the cheaper CatEye LEDS (EL-110 I think) for a year or so now.
The battery life is great (on 4 NiHM AA batteries, I can go months wi/o recharging, using the light maybe a couple hours a week), but the brightness is not very impressive. The beam is very small, and barely visible under streelights. If it gets really dark, I can kind of use it to see the road, but I have to aim it close to the bike and go slowly. However, it's good enough to be seen by cars, and I've found it adequate for riding on well-lit city streets.

I'm not sure how the brighter CatEyes compare.