I ran a 1/2 marathon over the weekend, part of which took place on a very wide 3-lane highway. I noticed that most of the runners were sticking to the far-right lane, as if they were driving in a car. This put them on the outside of some long sweeping corners.
However when they measure a course, they actually use the shortest path.
How do you figure out the shortest path? Look far ahead to where you're ultimately trying to go and race toward it. This will typically mean making as straight a line as possible from the inside of one corner to the inside of the next.
Of course, you don't want to be cutting people off, so be aware of who is on your right or left... I'm looking at you, Mr. iPod!!!
How much can this save?
The better question is - how much is taking the long way costing you! Every extra step you take is a step away from your goal time, or worse, away from a Boston Qualifier.
The cost depends on the course - it is highest on a wide course or one with many corners, lowest on a narrow straight course. Once you have your mind dialed in to take the shortest path, though, you'll find you naturally gravitate toward it and it's really just "free speed".