Virtualbox 4 install on Ubuntu

Since the default Ubuntu repository does not have the current version of VirtualBox (currently 4.1.x) here is the installation procedure via apt-get

echo "deb $(lsb_release -sc) contrib" | sudo tee /etc/apt/sources.list.d/virtualbox.list
wget -q -O- | sudo apt-key add -
sudo apt-get update
sudo apt-get install virtualbox-4.1

To use USB devices on the clients you need to install the Extension Pack from the Oracle Site and install via the File –> Preferences.