Device: Droid Bionic
When trying to start a new creative world, the 'generating terrain' screen displays, progresses to about 90%, and freezes.
When trying to start a new survival world, the 'generating terrain' screen displays, you enter the world, and just as your feet hit the ground the screen goes to a solid green color.

You can't back out of the 'generating terrain' screen, you have to exit and force close MCPE in settings/apps.
You can back out of the green screen, and it returns to the main screen. After restarting or returning to the main screen, the new world you tried to create is listed in the worlds. When you try to open it, the message "can't open xxx world" is displayed.