Wasn't someone just laughing that XboxOne couldn't even get Youtube... and here it is coming to the 3DS.

I wonder if they will bother to add support for 3d videos that are already on the site...

It about time that we'll be able to watch YouTube on the Wii U touch screen and that it's FINALLY coming to the 3DS also. And as for playing 3D videos that are on YouTube on the 3DS I can't see why not, (but I could be wrong). (However with Nintendo's record of NOT bringing it all to the table I won't count in it.)

You tube 3D is for 3D glasses isn't it? like Red/blue glasses?

last time I tried to view one, that was how it worked, but that was a mighty long time ago.

Good! Not really needed for me, but for many (kids) I can see it being a gateway to YouTube.

This nearly makes up for letterbox :D

No.  You tell YouTube what kind of 3D display you have, and it serves the compatible video.  It transcodes 3D (and automatically converted) videos to the various supported formats.