Back in May of 2008 I did a post on how to taper for a marathon (The Taper), citing research that recommended reducing weekly miles by 75%- 50%-30%-15% over 4 weeks, doing pretty much nothing the last week other than a progressive decrease in the number of high intensity intervals.
There is more. According to Owen Anderson, a 150 second all out effort followed by a 30 second all out sprint THE DAY BEFORE YOUR MARATHON causes your muscles to quickly supercompensate with glycogen so you are ready to go by race time (it goes without saying you need a high carbohyadrate diet for this to work) Glycogen without glucose gluttony: your new carb strategy for optimum performance.
In case you missed it, researchers at Ball State University (my alma mater) have taken another look at the taper ( Myocellular basis for tapering in competitive distance runners). Amby Burfoot summarized the findings in layman's terms at Runners World Peak Performance
According to Burfoot, Ball State researcher Scott Trappe recommends the following (keep in mind this study used an 8K distance for their test- not a marathon):
3 weeks before race: Do 75 percent of normal "midseason" training. Eliminate most medium-hard runs. Do usual interval training.
2 weeks before race: Same as above.
Last week before race: Do 50 percent of normal training. Eliminate virtually all medium-hard runs. Do 50 percent of usual interval training.
Trappe warns that runners have a tendency to do more tempo runs when they cut miles because they feel so fresh (I will attest that is 100% accurate!)- he recommends cutting those hard miles out so that you only do easy miles mixed in with your interval workout.
I wonder what percentage of marathoners actually DO intervals? If you follow the 3-day a week plan recommended by Run Less Run Faster, than I guess that means you'll either drop the tempo day or substitute a short interval workout.
Like anything else, it's trial and error, and don't try anything before a race that you haven't experimented with before.