| Let me throw some fuel on this fire.
Why is Neptune a planet? It hasn't cleared it's orbit. It fights for the same space (literally) as Pluto. I will agree that Pluto and Neptune are locked in a 3:2 orbit ratio so they are never in the same space at the same time. But I don't see anything in the definition about timing.
Jupiter shares its orbit with an entourage of asteroids that follow and preceed it by about 60 degrees in its orbit. These are called "Trojan" asteroids. Gravitational nudges from other planets sometimes change the membership of these clusters, tossing some out and introducing new ones, but the definition doesn't say how long an object has to share an orbit to consider the orbit as being shared and not cleared.
For that matter. Earth hasn't done such a good job clearing it's orbit either. Ask the dinosaurs. OK, so collisions of that maginitude only happen every tens or hundreds of millions of years. Suppose they only happed every million years, or thousand, or hundred, or annually or twice a month? Should we cancel the NEAR project because, as an official "planet," Earth is by definition, clear of other objects? Again the definition is lacking.
The best "suggestion" I've seen includes relative mass. If an object has more than 1,000 times the combined mass of all the other objects with which it shares an orbit then it can be considered as having cleared its orbit. Then the debate becomes what number do you pick, 10, 1,000 or 1,000,000?
This "modification" to the definition allows Neptune to be a planet while Pluto is not even though they have intersecting orbits. | 
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