Someone tried a minecraft clone in Unity too, it's called cubelands and can be purchased as well but as far as i know it doesnt support stuff like water or crafting yet.

Though the graphic is nice.

And i if i remember correctly, they group cubes of the same type to a new one, by creating meshes at run time. So there are only a few drawcalls actually and its pretty fast.

As a game designer i am also interested in trying something like minecraft (i mean to program it)

I would be more interested about the landscape generator though. I wonder how he gets the nice mountains and cave systems. I also read that the new generator (that create stunning mountains and structures) was actually a bug, he just kept it cause it looks better.