PSA: Miiverse for 3DS is now live!
If you want to follow me my handle on Miiverse is Kohakuchan.
You can also find it here on the website:
Miiverse is pretty awesome and I recommend that everyone checks it out.
UPDATE: There is also an update for streetpass.
You can also post screenshots to Miiverse with the 3DS. To do this suspend the game with the home button. Then open Miiverse and hit post. Choose a screenshot (top or bottom screen) then add some text or a drawing and hit post!