Cracking first post Dawn, if I didn't know better i'd suspect you're a mischevious forumite on a wind up. But just in case you aren't, you've geniusly stumbled on perhaps the most repeated thread in RW history.
You get your staunch pro and staunch anti Ipod camps. Pro say they aren't affecting anyone, they can hear instructions, they're not a hazard to anyone, and it's their preference to run with music, as it's...easier.
The anti camp react furiously to such a notion, saying how can you possibly be fully aware to instructions, possible hazards, and generally arsing about in someone's way.
My own view is that I can see why listening to music eases things along. I run every single training run with music on. But then I would never dream of doing a race with an ipod. How are you possibly meant to run at your optimum level with a distraction like that? You can't feel your breathing as much, you're not as aware of how the race is developing, and you can't hear anyone about to come past you!
When I marshall a half marathon each November, giving encouragement to ipod wearers is a waste of time. They can't hear you saying encouragement any more than they can hear you saying vital safety instructions.
so you have to just let them risk it frankly!