re: gal_background local variable. If the gallery item has an image attached, then it's the gal_background, otherwise, it's the placeholder image. Currently, gal_background is set, and the gallery iterator uses it to define "style: background-image: url(?)"

gallery.html.haml

  %ul.thumbnails
    - gallery.each do |gallery_item|
      %li{ class: "span8", id: "#{new_sibling}_#{gallery_item.id}" }
        - if gallery_item.image
          - gal_background = "background-image: url(#{gallery_item.image.url(:gallery)})"
        - else
          - gal_background =  "background-image: url('/assets/empty.jpg')"
        %div{ style: gal_background , class: "cutter thumbnail" }
          %h1
            = link_to gallery_item.name, [parent, gallery_item]
            %small
              = "#{gallery_item.description}"