Nero 6 contains a 'bug' that could delete your entire harddrive. The bug is introduced with the Nero 6 Recode project. Bug might even not be the correct word for it, it seems more that Ahead forgot to limit the feature to empty the destination folder for temporarily files.
If this destination directory is set to the root of a disc (e.g C : \) and if the question: "Destination folder is not empty, do you wish to clear it" is answered with yes, all files will be deleted. Ahead has already put up a page explaining the issue that will be resolved with a future patch.