New Super Mario Brothers Wii has been out for, oh, about 48 hours, but the Wii homebrew scene is already on the case: GBAtemp user Tanks has recreated Level 1-1 from the original Super Mario Bros using a NSMB level editor called Reggie!, developed by a user named Treeki.
I don't know much about homebrewing or modding, but I do know something cute and nostalgic when I see it. Level 1-1 is kind of played out by now—if a level editor exists for any game, it is a divine rule of the universe that Level 1-1 must be recreated—but it's an impressive, and rather hasty, effort nonetheless. The framerate is totally buggered (probably because it's running in a Wii emulator), but I'm not one to judge.
Like I said, this isn't really my area of expertise, but if you're interested in Reggie!, you can check out more details and screenshots here. So far, it features sprite, object, and block editing with more coming soon. I have to wonder if that includes Super Guide functionality, although I doubt it.