The New York Times has an article on the run-walk method (Better Running Through Walking). As the name implies, this method consists on taking walking breaks while running, whether during training or racing. Practitioners enjoy this method because it makes running less grueling and reduces the risk of injury. At the balanced athlete, we highly recommend this method to beginning runners. However, experienced runners can also see benefits and even improve their times at races. One of the reasons why this method works is because it helps to maintain an optimal heart-rate training zone (I am sure you have heard this before if you have talked to any of us at the store!).
Jeff Galloway's site offers lots of information on this method (Walk breaks?).
The NYT also has a new wellness blog focused on marathons: Marathon Well-Blog. It is worth a read during a lazy Sunday afternoon.