We are quickly coming up to the end of 2007, and if you want to make sure your blog is safe from anything that could possibly happen, from hackers tampering with your site, to data loss with you host you will want to back up your WordPress site, and doing so has never been easier.
The most basic way I would recommend would be using the built-in Export tool that WordPress now ships with, and export your blog in the WordPress eXtended RSS or WXR file type. You then only need to back up your wp-content folder, and your wp-config.php file. This should contain nearly everything you need to restore your blog if anything happens.
There are great WordPress plugins for backing up your blog, as well as online services that attempt to help you out as well. You can also back up your files and databases through cPanel. I highly recommend using multiple methods and keeping backups in multiple places. Sometimes even just having a cheap hosting account with another company that uses a different data center is a great place to keep your offsite backups.
There is no excuse to not back up your WordPress blog if you are serious about blogging!