Just a quick correction - since the Boston Marathon is a USTAF certified course and one of the 5 courses in the World Marathon Majors, use of headphones is actually prohibited, a fact which the race packet will remind racers of. Of course given the large 30,000+ field, race monitors usually only monitor the elites, but as I ran the marathon last year, let me say that you don't want to use an iPod or any other device that will interfere with experiencing how amazing the crowd support is in this race. Good Luck!