Once you have a website up and running there are many reasons to have a local backup available.  Having a local backup will protect you from future issues such as server failure, outages, site transfers etc.  We recommend that you backup your website at a minimum once per month.  Most control panels have backup wizards or other tools to help you, but at a bare minimum you can FTP all of your files down and zip them up on your computer.  Another great tool is to setup backups remotely using a separate service just in case you lose your data on your local backup, change machines etc.  A few of the best services we have found are:

ElephantDrive

Elephant Drive- Backup Storage and Anywhere Access

Elephant drive offers a free trail for 15 days in which you can backup unlimited numbers of files with a max file size of 1GB.  It has automatic backup features as well as web access and costs just $49.95 for a year of service (or $4.95 monthly).

Mozy

Mozy is another great service offering that provides you with 2GB of backup space for free.  If you need more than 2GB you can purchase a yearly account for just $4.95 per month.