Blogs are great tools to record your thoughts and ideas for posterity. There's only one problem: Posterity could be interrupted by a server crash, which could not only take your blog offline but wipe out your hundreds of pithy blog posts.
You want to back up your blog, then. One way to do so is to use a specialized tool, such as BackupMyBlog. This service is for people who run their own servers, so not (yet) for users of hosted solutions such as TypePad or Blogger. Once hooked into your blog, it regularly copies your posts to two separate locations, either of which can be used to recover your data should you need it. (Found on SolutionWatch)
Or, here's an alternate solution: Every few months, or once a year, print a book of your blog. Use a service like Blurb, BlogPrinting, or BlogBinders to print out a nice archive of your work. It won't help you rebuild the electronic version of your blog, but it is something you can pass along to your children, long after blogs have faded into history.