Your collection of pocket monsters is potentially at risk.
A small number of Pokémon X and Y gamers are reporting that saving in a certain area of the world causes the game to freeze, and rebooting the 3DS does not fix the issue. After the initial bug, the game loads the save and then immediately freezes again.
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The Pokémon trainers reporting this bug claim that it happens when saving in the outside streets area of Lumiose City, one of the major hubs. The error causes Pokémon X or Y to hard-lock, and the player can only regain control of the system by holding down the power button. You can see how the game freezes even after loading the save in a video uploaded to YouTube:
A few gamers reported the issue in a thread on gaming message board Gamefaqs. The glitch seems to affect both digital and physical copies of both X and Y. Until Nintendo issues a patch, it is probably wise to avoid saving in Lumiose City.