The idea is to get people to write only about science for one week, from February 4 - 8. They will have an RSS feed set up, and anytime someone who has signed up to blog about this makes a post, a reader can see the post. In other words, get the RSS feed and all you will see are science posts from various bloggers for one week in that feed.
I think this is an interesting idea, but I'm ambivalent. There is almost no information on the site on why they are doing this, and no info at all on who is behind it. Perhaps some bloggers who don't post very much will be interested in signing up to blog, but that doesn't appeal to me. Like any scientist, my interests are wide-ranging, from astronomy to political nonsense to Doctor Who. I post on science topics well over half the time (despite protestations by people who, I suspect, just don't like it when I say something they personally disagree with), but all the time? That's not who I am. There's not much chance I'll stick to pure science for my four or five posts I make every day.
Ironically, starting Monday I will be in Austin for the American Astronomical Society meeting, and I will be blogging as much as I can with astronomy and space science news (that'll start in earnest Tuesday morning, but don't forget the blogger meetup!), so I actually will be doing quite a bit of science posts. But if I wanna post a picture of a LOLcat, I'll do that too.
Even more ironic: the post you're reading right now isn't about science.