We didn't learn much more about Pluto, other than it wasn't as unique as we once thought. We learned a lot more about other bodies in the Kuiper belt though. By our old classification, suddenly it looked like there could be hundreds of "planets" in our solar system. Our improved understanding of the nature of the Kuiper belt and its inhabitants caused us to reassess which types of features were useful to distinguish a planet from the vast number of smaller objects in our solar system.
