This question came to hanut me this past week, I was listening to Joseph and the Amazing Technicolor Dreamcoat on my MP3 player while working around the house. At one point I needed to go to the bathroom and, without thinking about it, continued to listen to Joseph.
Now, I don't want to say that Joseph is a "davar sheb'kedusha;" I'm fairly certain it's not. But it can very easily lead one to think about the personages and the story involved -- and that clearly DOES count as divrei Torah.
So, where does one draw the line between the secular and permitted and the holy and the not permitted? When the secular and the holy are sort of mixed in this fashion, where is the dividing line.
(Related question: Can one