...is that they will be able to be toggled with redstone signals! Imagine, a light switch in your house that turns on all the lights! Or outdoor lights for when it gets dark. Or pressure plates attached to lights so you know when something is around!
Notch has stated that there will be a redstone-activated light. Actually, he hasn't quite confirmed it... I think he was replying to the "will torches become lanterns?" question, and not necessarily the "light bulb" question... Hmm, hard to say.