Ubuntu Unity Plugin for compiz comes default in Ubuntu 11.04, it helps changing unity behaviours and makes a good experiencing. Here’s how to enable or disable auto-hiding unity sidebar launcher with the plugin.
First of all, install the Compizconfig settings manager from Ubuntu Software Center or just run following command:
sudo apt-get install compizconfig-settings-manager
Start it under System -> Preferences menu, find “Ubuntu Unity Plugin” and click into its configuration page and see the settings in picture.