Section 230 of the Communications Decency Act protects platforms from responsibility for what their users post, this is the defense that http://www.dirtyphonebook.com and unvarnished and others of that ilk are taking.
LinkedIn is the Douches who went to school with you and sucked up to the teacher but had no skills. OkCupid is the people who used to smoke in the bathroom during lunch. And http://www.dirtyphonebook.com people are the guys who got kicked out of school after the 5th grade.
I use Sass because it provides certain features that CSS doesn't ordinarily provide. (variables and mathematical computations for instance)
HAML provides (at least to my knowledge) nothing other than somewhat cleaner syntax. That to me isn't worth the pain of something not working or other developers not knowing HAML and not being able to be brought up-to-speed on a project too quickly
That's pretty sad because there are still some great mac apps being produced. Pixelmator for instance is a world-class product that deserves recognition.
Not a feature, but an actual unique concept.
The space is too crowded for wasting tons of time on another similar project.