Internet connection fails in Ubuntu on VirtualBox when virtual machine is created from "Import appliance"
Problem solved on ServerFault: https://serverfault.com/questions/30889/virtualbox-cloned-ubuntu-server-network-error/30893#30893
rm /etc/udev/rules.d/70-persistent-net.rules and then reboot.
hmm. i'd look at lshw and check if the name of the network device has changed, and edit /etc/network/interfaces to match if it has. then ifup - no need for a reboot