I’ve not used Haml for anything ever, but I have used Sass for sites that I’ve coded by hand, though not with Drupal. With that in mind, I also haven’t watched these presentations, but I do remember the first one getting a lot of excited buzz at DrupalCon Chicago. Finally if you grow to love Sass, look into using the Compass CSS authoring framework that builds on Sass and makes it even more amazing:
The following presentations were made at the past two DrupalCons in the US:
DrupalCon Chicago 2011
Themeing Haiku with Haml, Sass, and Peroxide.
http://chicago2011.drupal.org/sessions/themeing-haiku-haml-sass-and-pero...
DrupalCon Denver 2012
Using Sass & Compass In Drupal Theming
http://denver2012.drupal.org/program/sessions/using-sass-compass-drupal-...
Beyond these, a moment’s googling will reveal a whole new world of themes and resources about using Sass & Haml with Drupal.
Comments
Excellent YouTube videos on SASS/Compass
Tim: thanks for posting this. Jeffrey Way, who does a yeoman's job of online training, has an excellent intro to SASS through to Compass on YouTube here: http://www.youtube.com/watch?v=b_-HLevIJbc&feature=relmfu He helped to orient me in little time flat.
I've built one project without Compass and one with. The one with is sooooo much better.
SASS vs. LESS blog post
Kyle (screenack) also mentioned this article to me in the parking lot as we were leaving Redhat last week. It's a good overview and mentions why he thinks SASS is better: http://css-tricks.com/sass-vs-less/