I was introduced to LESS earlier this year and loved it. When I had to rebuild my personal site this past month, I did it in LESS instead of CSS and probably cut my development time in half.

I'm never going to write raw CSS again.

I grabbed CodeKit, so I might try SASS the next time I'm building something on the web. I haven't really seen anything in the SASS vs. LESS shootouts that makes me go "dang I wish I could do that"; my CSS is relatively straightforward. Just having named colors, a couple color mixing functions, mixins, and nested syntax helped a LOT.