[grakic]

What are current options to optimize LESS files and remove unused mixins? And for the generated CSS, what are current options to merge shared rules and remove unused classes reported against a sample HTML?

[shadeless]

>What are current options to optimize LESS files and remove unused mixins?

Kolega, use parametric mixins without parameters: http://lesscss.org/features/#mixins-parametric-feature

For unused css I'd try this: https://github.com/addyosmani/grunt-uncss

[grakic]

I got this recommended for handling shared rules: http://zmoazeni.github.io/csscss/