It's important to remember to backup your address book. Think of how hard it would be to replace every phone number, address, email address and contact name if your address book was lost, your drive died, or the address book database became correct. If you are using a Mac, it's really easy to backup your address book as there is built-in functionality to do this. Just go to File -> Back up Database... you can then choose where to save the file. I'd recommend using a remote drive or a flash drive. Restoring your address book is just as easy. Just go to File -> Revert to Database Backup and point it to the latest edition of your backed up address database.