Smash Bros copies are apparently leaking into the wild already so beware of spoilers, don't know how much spoilers matter depends on what the story mode is like I guess. This also means that just like Pokémon and Super Mario Party before it that Smash Bros will prohably be available to pirates before paying customers yet again, when/if someone gets round to uploading it.
Nintendo need to fix these leaks, or at least do something! Piracy is one thing, but them playing the game a week earlier than people who pre-ordered is insulting!