Duplicate your Drive
To make a full backup to an external HD, follow these steps:
1. Select the external drive in the Finder and choose "get info" from the file menu. You will see an option to "ignore ownership on this volume." Make sure that this is NOT checked. If this is option is checked then your backup won't work!!!
2. Launch Disk Utilities
3. Run "repair permissions" on your start-up drive.
4. Click on the "restore" tab (in Disk Utility). Yes, it should be named "backup/restore" not just restore but that's how it is!
5. Drag-and-drop your start-up drive on to "source" and your external drive on to "Destination", go ahead and check "erase destination."
6. Click "restore". It is really backing up your drive on to the external drive, not "restoring" anything, but whose to argue with the folks at Apple.
That's it. Go have a cup of coffee.
When you come back it should be done. You may wish to select your external drive in the finder and give it another name, since it will now have the same name as your start-up drive and thus will confuse the system. Otherwise just unhook your drive and leave it till you need to do another backup. If you want to test it out you can go into the "start-up disk" preference pane in System Preferences, select your backup drive, and click "restart." It should boot up from the external drive as if you were running off the internal drive. Don't save anything here (this is just your backup drive), but look around to see that everything is working as it should be! If you are ever in any trouble you can use your backup drive this way and then "restore" to your internal drive!
What is it with OS X and documentation? Apple has a LOT of capabilities they don't market very well. I'm definitely going to try this one. I may partition my external drive so that I can image this to a boot partition and keep the rest for other uses. Also experiment with drive images. CarbonCopyCloner is another approach of course.