Since this has been going around lately, I should probably give my two cents. Basically what it amounts to is that Nintendo has filed Content ID info of their games with YouTube. What this means is that if you upload gameplay video of a Nintendo game, YouTube will automatically monetize that video, put ads on it, a link to where to buy the game, and take the money generated from that video and give it directly to Nintendo. People who do "let's play" videos are, naturally, pissed off because they want to be earning money off their videos, so they're calling Nintendo "thieves" for doing this.
I can see both sides to the story. I can see Nintendo as a corporation wanting to exercise control over their properties. On the other hand, "let's play" videos can often help new gamers find games they otherwise wouldn't have tried.
But here's the thing: Nintendo isn't the first company do this. Both Microsoft and Ubisoft do it already. YouTube has also had a long history of having music videos and TV shows Contend ID matched to prevent users from profiting by uploading content that isn't theirs. In other words: Content ID matching isn't anything new, it's just the news that Nintendo is throwing their hats into the ring as well.
That's the bigger problem in my books. This is something ALL corporations are going to try and do eventually. I'd be surprised if, by the end of this year, pretty much every video game corporation out there hasn't filed for Content ID matching through YouTube. To me it seems like the next easy way for big corporations to earn "free" money.
But just so you know, YouTube states in their terms and conditions the following:
"You may not be able to monetize videos which use any of the following without the explicit permission of the person who created or produced all material: Including Video game or software visuals"
So by YouTube's own standards, "Let's play" videos are against the rules ANYWAY.
Again, I see both sides. I personally feel that this is a big mistake on Nintendo's part, but I also can't really fault them for trying. They're not taking the videos down. They aren't going to flag your account. And they're only targeting videos of a "certain length." So this likely won't affect smaller users who upload a quick "Let's Play" here or there, but more likely to affect the bigger YouTuber's who have hour long videos showing every detail of their games.
So, no, Nintendo is not "stealing" your money away. Chances are you won't even be affected by this even if you upload Nintendo related content. But it's still a problem and Nintendo is just one of the first to do this. More will come. And this is how things will evolve.