Tyler Hall at Sitening provides a detailed account 
of his backup strategy.
He divides his data up into six categories depending on how frequently he backs it up and how he does it.
Email backups, he writes, are all taken care of by Mail.app. He downloads all this Gmail into Mail using Gmail’s POP access and all his IMAP emails are mirrored in Mail.app’s local cache.
Preference files, the ~/Library/Mail and ~/Library/Mail Downloads folders, which are essential parts of a sensible Mail.app backup plan, are taken care by another backup process.
SuperDuper (”Heroic system recovery for mere mortals”) is the backup app of choice.
BackityMac is clever utility that offers pre-set, one-click settings for backing up your Mail, iCal and Address Book data into a disk image—
Bob at Google Blogoscoped 
