It depends.. I've worked with LESS, but now I'm back to vanilla. The ongoing project I'm working isn't that complex, so a preprocessor isn't that necessary.
I'm hoping that variables and mixins will come to CSS nativel! :)
That's probably the most common excuse I hear from people in real life and this mindset truly throws me off. Variables and mixins are only a part of the efficiency of using a preprocessor though, what about nesting?