I use Time Machine to create hourly back ups onto one drive.
I use SuperDuper to clone my hard drive every night at 3am to a bootable volume (Time Machine backups are not bootable)
I have a media hard drive that SuperDuper also mirrors to another hard drive after it's done backing up the main internal.
Why?
Say my laptop is stolen, and my external hard drive with the back on on it fails? Then the back up of my back up will sort me out. Yes, unlikely, but you never know. Two types of people in the world. Those that have had a hard drive fail on them, and those that are going to.
Oh, and I also use Mozy online offsite backup for the essential business files in case of house fire etc.
I am one paranoid motherfucker.
But I know my data is safe.