Nintendo is going to make a pretty odd move with the upcoming update for the Photo Channel. Engadget reports support for MP3 files will be dropped while AAC support will be added:
Apparently, the aforementioned channel will be revamped early next month, and while users will then be able to personalize their menu by implanting an SD-based digital image into the Photo Channel icon, gamers who previously used their Wii to play back MP3s will no longer be able to do so. For whatever reason, the Big N will be axing MP3 support and adding in AAC compatibility, and the company even goes out of its way to make sure that you realize downgrading will not possible once you install v1.1. Mark it down folks -- don't be left full of regret (if you're partial to MP3, that is) after carelessly downloading an update without reading the changelog first.