Methods to detect a public IP address in Bash

As part of an installation script, I want to make an "educated guess" about the machines **public** IP address. It should be as robust as possible, working on a variety of hosts and platforms. Here is an example: https://gist.github.com/4669037 This script uses three methods and then defaults to the value of */etc/hostname*. I have only tested this on Ubuntu so far. Will this be likely to work on other distributions? And are there additional methods that I could add?