This is the key point.  You save time working with Haml and Sass if your designers can use them, edit them, etc.<p>I am longing to get to a point where the designers I work with can be expected to write templates using mustache or django template language...<p>Ideally the designer can check out a submodule of the project and commit ongoing UI enhancements by simply modifying mustache/django templates that they wrote in the first place.<p>This could easily be implemented by using a static site generator to populate the templates with static data so that the designer could check his/her work before committing.<p>With Haml you end up translating the whole mess over and over again, and if you decide to make a big change to HTML/CSS you are spending lots of time redoing the HAML/Sass.<p>The other key thing to realize is that CSS is an extremely expressive spec when used properly  I really don't think that the small bit of conciseness offered by Sass is worth adding another layer...