Here's the blurb from the initial post:
We wanted to give you a quick heads-up about an initiative we're starting on our Facebook page today. It is an interactive story that you can help us write! We post a screenshot and a poll, you help us decide what happens next. Muse has posted more info on our forums, so come take a look: link
And here's the first paragraph of the first post:
You bolt awake in an unfamiliar place, sweating and out of breath from the dream. You were in the tower again. The decay. The filth. And the Tuatha…. Panic. Fire. The gnome giving his life to save yours. So many dead. As you wipe the sleep from your eyes, you swear that you can still smell the moldy decay of Allestar Tower and the smoke of the fires that destroyed it.
It reminds me of things like Action Castle, which is kind of an interactive fiction party game. Oh, here's a great video: I was actually in the audience for this!
(edit: I see that the embedded video didn't get displayed for Planet IF readers -- here's the link: The "Action Castle" Incident at PAX East 2010)
Anyway, this is like that, but with thousands of people on Facebook. Neat!