Those Donovan-style breakfalls are amazing. I had heard about them, but hadn't seen them until I went to a dojo up near Albany where a couple of people were doing them. They're simply lovely. I got a lesson in them, but I'm still a long way from knowing how to do it. Jun was right about the serial landing. Another way of thinking about it is like taking a roll, but instead of starting the roll on the front hand (the one close to the ground) you want to start it on the back hand. The forward roll goes diagonal from front hand through to back foot. This one goes along the same side of the body: from back hand to back foot.
One hint that I got was that it takes a lot of abdominal involvement.