I'm writing Regdel, another open source bookkeeping and accounting program in Ruby using the Sinatra framework.
Sinatra supports Sass templates, so I decided to give it a try. I was a little skeptical, because Haml, the HTML template system by the same creators, is not right for me.
I'm glad I tried Sass. It is quite nice, actually. It has a "Ruby-esque" feel to it, and thankfully it doesn't detract too much from CSS strength.
My one complaint is that it works off of Ruby's symbol syntax instead of CSS param-value syntax. For example, instead of this (CSS):
width: 500px;
Sass uses this:
:width 500px
It will just take some getting used to.