This Runners world article http://www.runnersworld.com/article/0,7120,s6-241-285--11154-0,00.html recommends active rest (stretching and light cross training) the first week after a marathon, and a return to running only the third week after the race.
Easier said than done. While I was too sore to think of running for the past 3 days, this morning, I woke up ready to return to the routine. This evening, I tried a more vigorous stretching session, and slight pin pricks in my back, knee, achilles tendon and mid-sole signalled me that I am probably jumping the gun. I had to appease myself with 12 very low-intensity minutes on the exercise bike.