Very useful
I honestly signed up to Newgrounds to write this review.
Yes, Minecraft creates a random seed when you create a new world. But which is easier: Creating a world, opening NBTedit, navigating to the folder, opening level.dat and extracting the seed, or pressing "Generate" and copypasting into both Minecraft and a text document?
I generally just use the name of whatever song I'm listening to, but if I'm playing Minecraft without music I'll use this.
Oh, and showing a preview of the map would mean that he has to use Notch's code, which would be breaking the law.