The Large Hadron Collidor goes online today! This is as exciting as the day Hubble opened its shutters May 20 1990.
Even a lot of sciencey people I know have been asking about what the LHC is, and why the doomsayers are wrong, so here's a little summary of it. Particle accelerators (as is the LHC) are devices that smash things together to find out what's inside them. It's somewhat like if we wanted to learn how cars work, so we did head-on crash tests. While the analogy isn't perfect (no analogy ever is), there are some similarities. For example, while head-on crashes in real life are dangerous, crash tests are completely controlled and are entirely safe. Particle accelerators let us learn about what's going on inside small particles. Older lower energy ones smashed together "normal" particles like electrons and protons and helped us to learn that those are made of quarks. The LHC is a high energy one and we'll be smashing together another type of particle called a hadron, and it will help us learn how the entire universe works, for example gravity and dark matter.
The woo-hoos (aka tinfoil hat wearers) have been saying doom and gloom about the LHC, claiming that the high energy levels will either rip a hole in the entire universe, or else create a black hole that will swallow the Earth. Well, there's really no reason to worry at all. First off, we only call the LHC "high energy" by comparison - it's higher energy than anything people have been able to do before now. However, much higher energy collisions take place every second as cosmic rays hit the Earth's atmosphere. The main difference is that in the LHC these collisions are controlled. As I said to a biologist in another community, being afraid of that is kinda like if people were afraid of scientists culturing e.coli - it happens in the wild, after all, and that's not scary at all.