With Mac OS X Lion and a new piece of free software, it’s easier than ever to create a USB keychain that you can boot from. It’s also extremely useful for keeping your basic setup consistent across multiple computers, if you find yourself switching hardware regularly and I’ve had fun in the past setting up a bootable USB keychain loaded with all the apps and files I need to turn any Mac-compatible computer into a viable media center quickly and easily.
A bootable Mac OS X thumb drive comes in handy when you need to troubleshoot OS issues for yourself, your family, or your friends.