I'm trying to decide if I should include Compass when starting a new Rails 3.1 project. I haven't used Compass before.
Rails 3.1 now supports SCSS directly. The Rails 3.1 asset pipeline (via sprockets) now compiles stylesheets automatically. And I can use a SCSS version of a CSS framework such as Blueprint directly.
What benefits will I get from using Compass with Rails 3.1?
Bourbon (by Thoughtbot) is a light alternative to compass that integrates well with rails 3.1.
It has the main css3 mixins you get with compass (background-images, box shadow, border radius, gradients...). It also has helpers to style buttons, "gridify" your layout and a few more goodies.
You might miss some of the power features compass has, but that can be easily overcome with the power of sass : just copy/create you're own mixin!
Compass often gave me headaches when upgrading my rails app. I appreciate the simplicty of Bourbon (although it might give you headaches as well... in the morning :-) )