Nintendo has detailed a game-breaking bug in The Legend of Zelda: Skyward Sword, and given tips on how to avoid it. Please be aware that Skyward Sword spoilers will be below.
The bug only happens if you complete the Song of the Hero quests in a certain order:
1. At the beginning of the quest, go to Lanayru Desert to retrieve the song of the Thunder Dragon.
2. In the Lanayru Mine, speak with Golo the Goron.
3. Complete the Thunder Dragon’s event, and receive his song.
4. Before heading to the forest or volcano regions, speak with Golo in the mine again.
5. At this point, the forest and volcano events will no longer occur, making it impossible to continue.
The only way to finish the game will to either load up an earlier save, or start again. Needless to say, if I had to start again after 30 hours of gameplay there probably wouldn’t be a Wii left to play on. Or a TV. Or the living-room window. So, DO NOT go to Lanayru Desert first.
Source: Zelda Informer