NPR is featuring this. Generally, ideas like this appeal to me. Ideas. In execution, I find her voice annoying. Admittedly, the main one I listened to was the "Psycho" title-sequence theme, which is intended to get on your nerves.
The fact that it can be done isn't enough. You have to do it well. Check out the Swingle Singers to hear what this replacing-all-the-instruments-with-voice thing can be like at its best. Something about the sound of it makes me feel like these people are too pleased with their ability to do it at all. I know: this may be a special delusion of mine. I simultaneously admire it and feel irritated. Is it just me?
In the case of Petra Haden, I feel really irritated.