According to Don Yeomans at NASA's JPL, the asteroid 2007 TU24 will miss us by about 530,000 km (334,000 miles) on January 29. It was earlier reported to be a distance of about 700,000 km, so it'll be a tad closer than earlier thought.
However, before some evil scaremonger runs with this, that doesn't mean OH NOEZ WE DON'T KNOW WHERE IT WILL BE! It means instead that we do know where it will be, better than we did before. It won't come anywhere near enough to hit us, and it will have no effect on us at all. It'll be hard to see; it's a faint 10th magnitude, meaning you'll need a big 'scope to see it.
Put it this way: asteroids pass us at this distance all the time, and here we are. No fires, no lightning, no earthquakes... at least, no more than you'd expect to occur randomly. Asteroids this size are only a problem if they hit us, or they might hit us in the future.
So, despite some very misleading tactics by people on the web, we're not in any danger. I'll have more on this later (by "this" I mean the scare mongering), too, since this has turned into a whole big thing. But I'm still right, and others still wrong.