If you plan on getting a shiny new Nintendo 3DS when it launches later this month, you should probably take care not to use flash carts to play ROMs. A report from GoNintendo claims that firmware updates may render the 3DS inoperable (aka "bricked") if it detects fishy activity.
Japanese retailer Enterking has updated its site with a warning about the possibility. The (very) rough translation states, "In case if you use equipment which is illegal or unapproved by Nintendo or if you do customization which is unapproved by Nintendo, there is a possibility that Nintendo 3DS become non bootable by system update."
In response to an inquiry, a Nintendo spokesperson told Shacknews, "We do not discuss product security details (for obvious reasons), nor can we discuss the details of countermeasures available in the Nintendo 3DS system."