68% is way too high. Most scientists are currently putting the chances of a hit around 40%. I don't think I need to remind you that life on this planet as we know it is going to be eradicated if an asteroid of this magnitude hits. It's overkill in fact. The environmental effects of one much smaller would be enough to obliterate mankind. It really sucks because we're not at the point yet where we can deal with asteroids of this size. We can see them coming, but can't do anything about it. In a few decades perhaps, but now we just don't have the capabilities. Personally I can't sleep at night because 40% is VERY high. I mean you have a 40% chance of not living through the end of the year. That sucks. Also if it doesn't hit this year it has a 70% chance of hitting us within the next decade. If we beat those odds, then we won't have to worry about this asteroid until it comes back around in the 24th century.
Man, it SUCKS.
EDIT: Don't know about you lot, but I'm maxing out my credit cards and going on vacations, because we have less than a 20% chance of living through the end of this decade.