The International Astronomical Union (mirror) has finally defined the meaning of the term "planet", and much to my dissapointment Pluto doesn't fit the bill. The part of the definition that it fails to satisfy is that a planet must have "cleared the neighbourhood around its orbit."
This brings to mind certain news stories that pop up once in a while about killer asteroids that might hit Earth. NASA has an active program to track "Near-Earth Objects". According to their website, there are at least 803 potentially-hazardous asteroids, and that doesn't even count the NEO's that aren't PHA's. Or maybe there are 4170 known NEO's. But regardless, I wonder, has Earth really "cleared the neighbourhood around its orbit" enough to fit the definition of a planet?