The Legend of Zelda: Skyward Sword -- say, around the "Song of the Hero" quest -- you'd better be careful. According to an email from Nintendo sent to Zelda Informer, you may encounter a game-breaking glitch if you complete tasks in a certain order during the "Song of the Hero" quest. If you save after the bug is in effect and don't have an earlier file as a backup, you'll have to start Skyward Sword over.
If you complete the quest's desert leg first and speak to a Goron gentleman not once, but twice, the game locks out completion of the other two portions, halting all progress in the game. That said, it's pretty easy to avoid: just don't talk to the Goron more than once. Done! (Alternatively, do not complete the desert part first.)
Nintendo gets more specific in describing the glitch in its letter, which we've dropped below the break. We've reached out to Nintendo to see if a patch will be issued for the game, but the company's official release unfortunately didn't indicate as much.