In the most recent Iwata Asks about Miiverse, Nintendo confirmed the screenshot taking feature that is built-in to every Wii U system-wide:

Kurisu: I want people to try Miiverse just by itself, and also try posting to Miiverse from games. If you spot a cool scene, you can post a screenshot by pressing the HOME Button. I truly hope people will actively participate in the communities tied to particular games.

Iwata: After you press the HOME Button, you can go from the HOME Button Menu to Miiverse. The game screen that was displayed at the time will be saved as a screenshot that you can post, right?

Kurisu: Yes. There’s a spoiler button, too. We’ve designed it so that people who don’t want to see spoilers won’t have to.

Iwata: There’s also a way to report something that you feel is a spoiler so it should be hidden.

Kurisu: Yeah. I hope people will make use of such features and enjoy aspects of Miiverse that connect to the games.

I remember Nintendo mentioning this before but I don’t think they confirmed it was for every game.  Looks like we’ll be able to easily take screenshots of all of our best/worst moments in games and send them to our friends.  The spoiler tag feature is nice too.

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