A month ago, I was reminded by a podcast of an article I read in runner's world a couple of years ago. The podcast was an interview of Bart Yasso, the namesake of the Yasso 800s - a workout described in the Runner's World article. Essentially, here's how it works - if you want to run a 4-hour, you do ten 800-meter intervals in 4 minutes, followed by 4 minutes of jogging. Apparently, it works for just about any time, and, according to Yasso, for about 95% of the runners he's seen.
So in my case, it will look like this: since I want to run a 3:40:00 marathon, I will run run two laps around a track in 3 minutes 40 seconds - 1:50 for each lap. You're supposed to start out with 4 intervals (4x800) and work your way up by adding one interval each workout until you're at 10x800 - that is, 800 meters in 3:40, followed by 3:40 of jogging, repeat ten times.
So while I have not set up my training schedule yet, I like the simplicity of this training concept, and will likely include it as speedwork.