Speaking to Hero Complex, Nintendo president Satoru Iwata revealed plans to implement three forms of filtering for Miiverse content. The first is algorithmic – automatic content filtering. The second is really, really hardcore: having a moderator read all posts before they're published. Finally, users can flag inappropriate content.
Iwata didn't say how long of a delay the moderation would cause, but he suggested "personally, I think 30 minutes should be acceptable."