From the WordPress.com FAQ blog:
Absolutely. If a very large meteor were to hit all of the WordPress.com servers and destroy them beyond repair, all of your data would still be safe and we could have your blog online within a couple of days. (After the meteor situation dies down.)
In the future you’ll also be able to download a personal XML backup of your data, but we don’t have a timeline on that quite yet.
Meanwhile, I logged on to the Backburner this morning to find all my posts from the weekend gone. When I logged in to the administration page, I saw a prominent red-boxed message up top that said something to this effect: “We had a major disk failure this morning and lost all the updates you may have made over the weekend. Sorry! You may be able to recover your posts through Google Blog Search or Feedster, but if you can’t, they’re gone for good.” They helpfully provided links to searches for Backburner content on Google and Feedster. The message is gone now, in its place something that implies the lost messages may be coming back eventually. We’ll see. I did manage to recover the old posts from Feedster — Google Blog Search didn’t have ’em — but I lost some improvements I made to my Bush post and any comments that used to be there.
Heh, I can hardly wait to see what the Flock Sucks guy has to say about all of this. All his posts are gone, too — he’ll probably interpret it as a plot against him.
UPDATE: Everything’s back now. The weekend posts on this page are the originals, not the recreated versions, which I’ve deleted. So I’ve got to give credit to the WP.com people, their initial panic and doomsaying aside.