.. Dawn will be delayed.
Seriously, the Dawn mission to asteroids Ceres and Vesta -- surely one of the coolest things NASA will have ever launched -- has been delayed until at least Monday. It was supposed to launch tomorrow, but lightning made fueling the rocket a little touchy.
You can read all about the mission and the launch schedule on NASA's Dawn page. I'll be Twittering the launch, and if you want some backstory, read how politics at NASA nearly screwed over this fine mission, and links in that page will give you even more info.