It occurs to me that I made something of a paternalistic assumption here: that people who do think they aren't harmed, or are helped, by music are simply wrong/mistaken about it. Perhaps it's simply that some people can handle the music and some can't, and I fall into the latter?

I'm glad to say that just today I saw media coverage of a study on multitasking indicating that people used to multitasking are both worse than singletaskers and deluded about it: http://news.bbc.co.uk/2/hi/technology/8219212.stm

So there! :)