Unfortunately it only implements the curly-brace SCSS syntax, not the indented SASS syntax [1] (which is weird considering it's called Libsass, not Libscss), and there are no plans to support both syntaxes.
The companies I have worked for all use the indented syntax, since it meshes very well with HAML and CoffeeScript. But it looks like more people use the brace syntax (roughly 980k SCSS files on Github, vs. 85k SASS files).