The National Fire Prevention Association and the Federal Emergency Management Agency have more than a lot of info about Christmas tree safety. I especially liked the videos of a dry tree going up in flames. It was insanely, mind-bogglingly fast. I knew dry trees were flammable, but this was amazing to watch:

"Within three seconds of ignition, the dry Scotch pine is completely ablaze. At five seconds, the fire extends up the tree and black smoke with searing gases streaks across the ceiling. Fresh air near the floor feeds the fire. The sofa, coffee table and the carpet ignite prior to any flame contact. Within 40 seconds "flashover" occurs -- that's when an entire room erupts into flames, oxygen is depleted and dense, deadly toxic smoke engulfs the scene."

Nothing says "Merry Christmas!" like flashover and deadly toxic smoke. Definitely have to make sure the tree is watered real well this year.