I am a gamer/LPer at http://youtube.com/ZackScottGames, and I can confirm that Nintendo is now claiming ownership of gameplay videos. This action is done via YouTube's Content ID system, and it causes an affected video's advertising revenue to go to Nintendo rather than the video creator. As of now, they have only gone after my most recent Super Mario 3D Land videos, but a few other popular YouTubers have experienced this as well:
According to Machinima, Nintendo's claims have been increasing recently. Nintendo appears to be doing this deliberately.
Thought I'd share this to the Neowin community to hear their thoughts on this, if this is indeed true.
Sounds like they want to have their cake and eat it too, so to speak.