For all the rails asset pipeline's issues and the grievances it causes, it makes it really convenient to use either Sass or LESS. The tooling integration is trivial to setup (add [sass|less]-rails to your Gemfile) and it compiles assets automatically. Also, browser hacks work fine [1, 2].
[1] http://www.yonbergman.com/2012/05/19/why-you-should-use-sass