Build your own Mario worlds

This, along with the slew of other announcements from Nintendo, has me really excited about the future of the Wii U.

It also scares me. I remember seeing videos of ridiculously challenging Mario stages created by modders (e.g. https://www.youtube.com/watch?v=3C1BSbq5aB0) and trembling in fear.

I think Sony announced LittleBigPlanet had something like 2 million user-generated stages? I hope we see something that big with this system, and hopefully a nice system around all the content so awesome content can more easily be fleshed out.