Install Sass on Heroku plugin.

app/views/layouts/application.html.haml

@@ -8,7 +8,6 @@
     = stylesheet_link_tag :all, :recursive => true
     = javascript_include_tag 'prototype', 'effects', 'builder', 'application'
     = javascript_tag 'Builder.dump();'
-    %script{:src => '/mint/index.php?js', :type => 'text/javascript'}
 
   %body
 

vendor/plugins/sass_on_heroku/README.rdoc

@@ -0,0 +1,7 @@
+= Sass on Heroku
+
+Rails plugin to compile Sass files to tmp/ and serve from there, avoiding trouble with read-only filesystems.
+
+It will add a Rack middleware on top of your Rails app that quickly detects requests for Sass CSS files, and serve them with caching headers.
+
+If you have issues please tell us on support.heroku.com -- or just fork it :)

vendor/plugins/sass_on_heroku/init.rb

@@ -0,0 +1,3 @@
+if RAILS_ENV == 'production'
+	ActionController::Dispatcher.middleware.use SassOnHeroku
+end

vendor/plugins/sass_on_heroku/lib/sass_on_heroku.rb

@@ -0,0 +1,74 @@
+class SassOnHeroku
+	def self.original_css_location
+		@@original_css_location ||= nil
+	end
+
+	def self.original_css_location=(location)
+		@@original_css_location = location
+	end
+
+	def initialize(app)
+		@app = app
+		initialize_sass unless self.class.original_css_location
+	end
+
+	def initialize_sass
+		# get the original location of compiled css files (ie: stylesheets/compiled)
+		# and replace it to a location in tmp
+		if Sass::Plugin.options[:template_location].is_a?(Hash)
+			self.class.original_css_location = Sass::Plugin.options[:template_location].values.first
+			Sass::Plugin.options[:template_location].keys.each do |k|
+				Sass::Plugin.options[:template_location][k] = css_location_on_heroku
+			end
+		else
+			self.class.original_css_location = Sass::Plugin.options[:css_location]
+			Sass::Plugin.options[:css_location] = css_location_on_heroku
+		end
+
+		# compile Sass once, and set it to not compile again
+		Sass::Plugin.options[:always_update] = true
+		Sass::Plugin.options[:never_update] = false
+		Sass::Plugin.update_stylesheets
+		Sass::Plugin.options[:never_update] = true
+	end
+
+	def call(env)
+		if !stylesheets.empty? && env['REQUEST_PATH'] =~ css_request_regexp
+			return render_sass($1)
+		end
+		@app.call(env)
+	end
+
+	def render_sass(name)
+		css_file = "#{css_location_on_heroku}/#{name}"
+		[
+			200,
+			{
+				'Cache-Control'  => 'public, max-age=86400',
+				'Content-Length' => File.size(css_file).to_s,
+				'Content-Type'   => 'text/css'
+			},
+			File.read(css_file)
+		]
+	end
+
+	def css_location_on_heroku
+		"#{RAILS_ROOT}/tmp/sass-output"
+	end
+
+	def stylesheets
+		@stylesheets ||= Dir[css_location_on_heroku + '/*.css'].map { |f| f.split('/').last }
+	end
+
+	def css_request_regexp
+		@css_request_regexp ||= build_regexp
+	end
+
+	# builds a regexp that matches requests for Sass stylesheets
+	# ie : \/stylesheets\/sass\/(file1\.css|file2\.css)
+	def build_regexp
+		files = stylesheets.map { |f| Regexp.escape(f) }
+		path  = Regexp.escape(self.class.original_css_location.gsub("#{RAILS_ROOT}/public", '') + '/')
+		regexp = Regexp.new("^#{path}(" + files.join('|') + ')(\?.*)?$')
+	end
+end