What difference does this make to anything, really? Apart from millions of textbooks needing to be corrected?

From Yahoo!:

Leading astronomers have decided that Pluto should no longer be classified as a planet. The decision means that the Solar System has been reduced from nine planets to eight. The International Astronomical Union made its decision after a week of heated debate at a conference in Prague.

They approved new guidelines which define what a planet actually is.

The new definition is: "A celestial body that is in orbit around the Sun, has sufficient mass for its self-gravity to overcome rigid
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body forces so that it assumes a ... nearly round shape, and has cleared the neighborhood around its orbit."

Pluto is automatically disqualified because its oblong orbit overlaps with Neptune's.

It has been put into a new category of 'dwarf planets'.

When the debate started a week ago, there were proposals to reaffirm Pluto's status and make planets of its largest moon, as well as two other objects.

However, the asteroid Ceres, which was a planet in the 1800s before it got demoted, 2003 UB313, an icy object slightly larger than Pluto, and Charon, the largest of Pluto's three moons, will not become planets.

Pluto was first classified in 1930 and at the time was thought to be bigger than Earth.

The eight planets which make the grade are: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.