I see what they've done there... and it's very smart. In fact, when I was learning CSS I always assumed it could support variables.

However, I'm not convinced that putting yet another layer between your code and the browser is worth the complexity. But then I feel the same about HAML. Obviously, lots of other people disagree.

I'd prefer to see these features in CSS itself rather than a separate technology

There is so many frameworks trying to circumvent css, may be css is crap ? Better than nothing but crappy still.

Adding extra layers is ok when we get more benefits than we loose in view. I'd like to have a better css too or a more programmable browser. May be will be able to rebuild a virtual browser within the canvas ... ?