Ruby on Rails 3.1 has been released on August 27, 2011. Reproducible: Always
Rails 3.1.3 is now in CVS. Parts of the recommended asset pipeline are also available, but at least sass-rails is still missing. I hope to add that tomorrow.
sass-rails is pending on sfl, which is not licensed in any way. We won't add this (and consequently sass-rails) to the tree until sfl's license is clear.
The licensing issue is with one of the test dependencies, so I've added sass-rails without tests. rails-3.1.3-r1 has a USE flag to pull in all default asset pipeline dependencies.