I've once lost a considerable amount of data, so I know to backup my stuff, but I suppose my solution is maybe a tad excessive:
- Full time machine backup on it's own dedicated external HDD
- Copies of all of my files on my NAS drive (separate from the external HDD)
- Copies of all of the important documents on a USB thumb drive I carry with me
- Dropbox account with all the important files (thinking about getting an F-Secure Younited account after Condoleezza Rice joined the Dropbox board of directors)
- Random backups of important data here and there
Used to have a full disc clone that I updated once a week, but I concluded it was beyond overkill with the time machine and other backups.