I like this point "Never use a mixin if you’re not passing an argument. Mixins without arguments are much better used as templates which can be extended." Which is a fair call I think.

However "Never nest rules purely for code organization. Only nest when the outputted CSS is what you want." is something I find harder to agree with.

If you don't do this then you're missing out on a ton of productivity from these tools and for what? Saving a few bytes in a CSS file that's going to be cached after the first request.

It's a pity we can't use Less or Sass directly in the browser in a reliable manner. CSS4 maybe?