Want to share my own story, hope it helps someone.
I'm an iTunes subscriber and there are gigabites of m4p files on my machine. Of course I used to listen to them on iPod. But last month my iPod was stolen (sh*t!) and I've got a new mp3 player on my birthday! Obviously I couldn't transfer my M4P collection to it because these file had iTunes DRM protection. Luckily I found MP4 converter and converted all my iTunes files just in few clicks!So I would recommend this MP4 converter if you have any problems with protected files - it will convert them to unprotected MP3 or any other format so you can use them without iTunes application.
The url is mp4-converter.info or something like this. Tell me if you need exact will go thru my mail