Wireless Energy Transmission

ScienceDaily reports on new technology being studied by Marin Soljacic, an assistant professor in MIT's Department of Physics and Research Laboratory of Electronics:

Soljacic is looking forward to a future when laptops and cell phones might never need any wires at all. Wireless, he said, could also power other household gadgets that are now becoming more common. "At home, I have one of those robotic vacuum cleaners that cleans your floors automatically," he said. "It does a fantastic job but, after it cleans one or two rooms, the battery dies." In addition to consumer electronics, wireless energy could find industrial applications powering, for example, freely roaming robots within a factory pavilion.

I've often thought that wireless energy transmission was potentially a huge field, but I could only think of two ways to make it work:

1. Transmission of the power in the form of microwaves/lasers, which had the drawback of possibly frying anyone passing between the power source and the target.
2. The use of "buzz lines"; a stream of tiny robotic insects that carried a tiny amount of fuel from some source. I don't think that's a serious contender, but it might work in a science-fiction story...