I couldn't post this in the Facebook comments on the post, but you can fix the Rake 0.9.0 error by putting the following right before load_tasks in your Rakefile:

    module ::MyAppName
      class Application
        include Rake::DSL
      end
    end

    module ::RakeFileUtils
      extend Rake::FileUtilsExt
    end

There's a fix on the way, too.

Also, I believe if you're using SASS/SCSS you can interpolate the asset like so, without having to use erb:

    background: #00ff00 url(#{asset_path 'rails.png'}) no-repeat fixed center;