I saw it used in a project once and it was a disaster. The problem being, by using javascript to represent html you are making your templates harder to write and harder to maintain.
This solution certainly has some cool features, but I strongly disagree with comparisons to haml. Where haml strips away a bunch of html syntactical weight, newt.js piles it on.
Sorry if i'm being too strong, but I just wanted to share my thoughts/experiences/criticism. It is clear the author has put a lot of work into this, including tests.
I like http://www.handlebarsjs.com/ for my javascript templating because I can literally cut and paste in some html into a template, add some logic(if/then blocks) and I'm done.