The nitty-gritty details:
"John Romanishin, who's been building robots and competing in robot derbies since he was a baby geek, figured out how to slip an itty bitty flywheel into the cube. It looks like a miniature desk fan that rotates up to 20,000 revolutions per minute — it comes with a battery, and when the flywheel is on, the cube has momentum: it can climb, roll across the ground, crawl up another cube, even leap through the air. "Which is pretty exciting," John says, "because it allows robots to jump on top of each other and go places that they couldn't go if they were only moving directly on the structure." "
Check it out on Robert Krulwich's blog:
And here's the MIT press release: