For the last few months I have been using one of the coolest online tools that you may not know about - BlogBackup Online.
I signed up for it and, quite frankly, forgot all about it. When I remembered it a few weeks ago, I checked in to find that yes, all of my blog posts have indeed been backed up on a daily basis. And then yesterday, I had the opportunity to really put it to the test; one of my other blogs was having major issues, so I decided to see if I could "restore" all of the backed posts to a new blog (on the same platform, but a brand-new blog). And, it worked! The only snafu was that the comments were not saved in a comments file, but were rather republished on the posts themselves (and you have the option of NOT restoring comments), but in my opinion, that's a small price to pay for recovering all my blog posts.
BlogBackup Online is, at the moment, in BETA and is FREE. It has an easy, intuitive interface, a very good help file, and works with all the major blog platforms. It seems far easier to use than some other backup tools and code-schemes I have seen. Even if you use WordPress and/or publish to your own server, I think it's still worth a look - when you work hard on a blog, you can't have it saved in too many places. And if you use a blog platform's free hosting, I think this tool could be a life-saver - not only in terms of archiving the content, but then being able to restore it EASILY. Check it out.