She's one of the few people who's live performance I've seen that blows away any recording I'd heard because of the sheer emotion that she brings to the stage.
I'm listening to her solo album at the moment, via Rhapsody. Most of it is very hootinanny, but ADORABLE.
See also: Nickel Creek, Sean Watkins, Chris Thile.
Oh, and here's a heart breaking rendition of Weezer's "Pink Triangle" by her brother Sean: