In the most recent "Iwata Asks" interview, Iwata talks with Kouichi Kawamoto about the Photo channel for the Wii. Aside for some basic Photobooth functionality, Kawamoto mentions an interesting tidbit: MP3's stored on the SD card along with the photos will be played in the background during a slideshow.
While this seems horrendously not cool, consider the fact that this functionality is in fact very similar to the Xbox 360's ability to play personal tracks during gameplay. In fact, a developer could most likely easily implement this functionality into any game they desire, so keep on the look out. If nothing else, it's an easy cop-out if Nintendo wants to add an extra "music channel" to expand functionality.