There have been several issues with Sass (sass-rails) and the Asset Pipeline. Some of them involving Compass (https://github.com/chriseppstein/compass/issues/516#issuecom...), some of them due to Sprockets (https://github.com/sstephenson/sprockets/pull/268#issuecomme...).

They have indeed been crippling for front-end development, and majorly under-reported since this summer. So if you're facing any of these issues, please participate in the GitHub Issues threads I linked above and help the relevant teams diagnose/improve the problems.