I'm surprised this hasn't been mentioned already, but then again, my search-fu is weak so it might have been.
Over the past week a commitee of the International Astronomical Union (IAC) have been meeting in Prague to come up with an official definition of a planet. The idea was to finally resolve whether of not Pluto was a planet or just a sizable lump of rock.
On Wednesday(-ish) they released their proposal. It's based on the gravity of the object in question and basically says a planet is round and orbits a star (and not another planet, 'cause that would make it a satellite).
This leads to their recommendation that the Solar system be increased to 12 planets.
The new ones being Ceres, largest rock in the asteroid belt; Charon, Pluto's 'moon'; and UB313 (aka 'Xena'), which is beyond Pluto. The interesting thing is that Pluto and Charon form a 'double planet' where the centre of rotation is between the two, so neither is the 'main' planet.
There are those opposed to the idea, including the discoverer of Xena, as it opens up the possiblility of tens, if not hundreds, of planets eventually being classified in our system, including several others in the asteroid belt.
It now seems as though in the next general assembly of the IAU that Pluto will be/has been dropped as a planet and be reclassified, along with Ceres and Xena, as a 'dwarf planet'. But then, the way these astronomers are acting, it could possibly change again.