Scientists define a planet as "A celestial body that is in orbit around the sun, has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit." Apparently, Pluto's orbit overlaps Neptune's (the nerve!) which is the disqualifying factor in this galactic quandary. But I propose the question: how do you know that Neptune's orbit isn't overlapping Pluto's?
According to USA Today, "The decision at a conference of 2,500 astronomers from 75 countries...[split] astronomers into factions, triggering days of sometimes combative debate that led to Pluto's undoing."

While I couldn't care less about how many planets are in our solar system (honestly, I've never noticed any of them) this is the kind of thing that really bothers me about science. Everybody is so sure that things are a certain way (guising it under the safety net of "theory") and then, in a single day, the solar system changes. Yesterday Pluto was the smallest planet in our solar system. It was fact. And now it's not.
Poor Pluto.