Chaitanya Adgaonkar’s recommendations for preparing your Mac for a Lion upgrade. This is his most important recommendation:
For those who want to take extra precaution, we recommend that you use SuperDuper. SuperDuper will basically clone your hard disk as it is to an external hard disk. The SuperDuper backup is also fully bootable.
I suggest that everyone takes the “extra precaution.” A fully bootable backup is much better than a Time Machine backup. Getting back up and running quickly is invaluable when your upgrading your OS.
SuperDuper! really is a fantastic application and my favorite way to do bootable backups.