The real story isn't that he was "caught", but that the Serbs agreed to hand him over. The Karadzic story was always about the struggle in Serbia between those that want closer ties to the EU, and those that want closer ties to Russia. There is no doubt that they knew all along where he was. He wasn't in "hiding", he was protected by sections of the Serb establishment.
His arrest doesn't really matter on its own. It's the fact that the nationalists lost this struggle that is great news. It's a huge achievement from the pro-EU Serbs, because they are a minority. It's good for the Balkans, and it's good for the EU. It might even help for Kosovo.