Don’t wait until you lose something. A hard drive can crash any time – even a solid state hard drive on your brand new Macbook Air (happened to a friend recently!) Just because you use IMAP and the email is held on your email server doesn’t mean you shouldn’t do backups. One would hope that your email service provider does backups too, but it is better to have control of your own life.
For example, at SaneBox we use Rsync, Crashplan and SuperDuper. Remember to test if your backups are really working by trying to recover something every 6 months or so. If you use SuperDuper, try booting off your SuperDuper drive. Tell us **your** favorite backup/disaster recovery solutions in the comments section, and we will aggregate that list and resend in a future Activity Report.