What advantages does Sass provide over regular CSS?

Question

I'm trying to decide on technologies for a presentation layer. I have heard Sass talked about enthusiastically but am resistant to learn something new without knowing why it's better than the alternative - in this case plain CSS. Any feedback on Sass would be welcome.

Edit: This is also a good discussion on this:

SASS: The Better, More Powerful CSS

Answer 1

I have a screencast that shows Sass and Compass (the Sass-based stylesheet framework) in action. It's an hour long, but it shows how Sass and Compass work and how they enable new ways of approaching website design by enabling sharing of implementation without compromising the content/presentation boundary.