She has an absolutely amazing voice, even live, which is rare for a pop singer these days. She nailed her performance last night. In front of such a huge room full of experience and talent, that's saying something.
Say what you want about American Idol, but at least it requires its singers to perfrom live, night after night. That's where the chops come in, and that's why American Idol is more compelling than the Grammys. Having said that, Clarkson's shelf-life will only be as long as the producer/songwriting teams responsible for her hits stay interested, which typically isn't much past 2 albums. (There's a reason Avril Lavigne now says she wants to branch out into acting).