Backing up your blog is important - and it has to be done as a specific task. You risk losing all those blog posts, comments, and images if you aren't routinely backing up your blog (or blawg).
Blogging Services Do Not Automatically Back Up Your Blog
I've had clients assume that their Blogger blogs were automatically backed up by Blogger. No, they're not. Blogger does NOT back up blogs. Neither does WordPress.
Website (and Blog) Hosting Services May Not Back Up Your Blog, Either
Whether or not your blog is being backed up routinely depends upon the service you're using. LexBlog, for example, does back up. Nice, and important to do, for a paid blogging platform.
However, I know of at least one web design company that promotes blogs as part of law firm website design but those blogs are not backed up. I learned of this situation because, sure enough, a series of law firm blog posts disappeared and there was no backup to fix the problem.
Easy Solution: HTTrack to Back Up Your Blog
There's a free service, HTTrack, that has proven to be safe and fast for me in backing up blogs. It has received good reviews from both CNET editors and users. (CNET provides a safe HTTrack download along with its review.)
You can also use HTTrack to back up your website - or really, grab a copy of any existing website or blog on the web - to save offline on your hard drive. This might prove handy for your website, your client's website, or perhaps a website that you might want to use in litigation ....
Daily Measure: Have Your Post Sent to Your E-Mail Inbox
Your blogging platform should allow you to automatically send each post as it is published to an email address (several addresses, actually). Make sure you take advantage of this safety measure, as well as periodically backing up your blog in its entirety.