Actually, I heard somewhere that anything orbiting a star is considered a planet in one sense or another... but that was before this whole "cleared the neighborhood" bull... Pluto, you'll always be a planet, in here *pokes chest*.
Definition of the "clearing the 'hood": The phrase refers to an orbiting body (a planet or protoplanet) "sweeping out" its orbital region over time, by gravitationally interacting with smaller bodies nearby. Over many orbital cycles, a large body will tend to cause small bodies either to accrete with it, or to be disturbed to another orbit. As a consequence it does not then share its orbital region with other bodies of significant size, except for its own satellites, or those governed by its own gravitational influence (such as Trojan asteroids).
Steven Soter of the Department of Astrophysics, American Museum of Natural History, has written that "A heliocentric body with Λ > 1 [viz., a planet] has cleared a substantial fraction of small bodies out of its orbital neighborhood."
The concept was used by the IAU in its August 24, 2006 redefinition of the term "planet" as one of the criteria differentiating a planet from a dwarf planet; a planet is a body with sufficient mass to have "cleared the neighbourhood around its orbit". The IAU also explicitly stated that Pluto will now be considered a dwarf planet; it has not cleared the neighborhood of its orbit (vis-à-vis Neptune and Kuiper Belt Objects such as the Plutinos).
However, Dr Alan Stern, who leads the NASA New Horizons mission to Pluto, contends that Earth, Mars, Jupiter and Neptune have also not fully cleared their orbital zones either. Earth orbits with 10,000 near Earth asteroids. Jupiter, meanwhile, is accompanied by 100,000 Trojan asteroids on its orbital path. "If Neptune had cleared its zone, Pluto wouldn't be there," he added.
Really, though, 2,500 people were so bored, they kicked Pluto's tiny, cold butt out of the planetary list just because it didn't do that? Thanks Dr. Stern...
Sorry for the long post, Bink. Just wanted to have some clarification brought to this...
-Marauder