As per the news GNOME shell will not be included in Ubuntu 11.04. Unity will be default desktop environment for Ubuntu 11.04. Here is the quick tutorial on how to install Unity 2D version on Ubuntu.
Adding repository
sudo add-apt-repository ppa:unity-2d-team/unity-2d-daily sudo apt-get update
Installing Unity
sudo apt-get install unity-qt-default-settings
After the installation, log out and log in again. At the time of logging in you will see Unity Qt option for desktop environment tab.
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The correct command to install via apt after adding the PPA is:
sudo apt-get install unity-2d-default-settings