I think there are some applications where people want music. It seems if it is a slideshow with *their* photos, they love it. Wedding photographers almost always set them to music

I have slideshows on my site and they all have music. You have to click them to play though. I had the one on my front page autostarting and got some negative feedback from those on slow connections.

As long as it doesn't accost me, I think music can be an ad