Mr Bruener is right, Lindy, these green bolides are rare, but nothing new. They've been around for at least decades, I remember reading about them in Sky and Telescope when I was a kid. In spite of their spectacular appearance, their motion is completely consistent with ordinary meteors, and except for their color, are exactly like all other bright meteors in their behavior. Of course, until we can actually find one on the ground and show conclusively that it is just a piece of natural cosmic debris, no one can prove without a doubt that they're not something anomalous. But the mundane explanation fits the facts perfectly without the need for speculation. The one conclusion we can draw with some confidence is that they are probably not re-entering orbital craft: they've been documented since before the space age began (see Hank's post below).