They passed a ruling this year that they can't ban Ipods or listening devices.  Alot of races like the Detroit Marathon frown on it because you can't hear what's going on around you.  They won't take your Ipod away.

I started running this year with an Ipod and quit after seeing an incident in a race.  We had finished a 10k and were walking back to the car.  Some of the slower 10k runners were still going and the 20k race had caught up to them.  The pace car was making announcements over a loud speaker to move to the left so the 20k leaders could pass on the right.  A guy had his Ipod on and couldn't hear them, even after 4 annoucements.  The pace car came up on him and he almost veered in front of the car and was almost hit.  He jumped off the road and went into a cussing rage with families all around when he was the one at fault.  It slowed the pace car down enough for the runners to catch it causing the leaders to become quite angry.

I too will be in the Detroit Marathon but probably will not be using an Ipod out of respect for the other runners and the organization.  Its a personal call though, you can use one if you'd like.