Auto Hi-res Sprites

icons.sass

@import compass

$icons: sprite-map("icons/*.png")
$icons-hd: sprite-map("icons-hd/*.png")

i
  background: $icons
  display: inline-block
  @media (-webkit-min-device-pixel-ratio: 1.5), (min-resolution: 144dpi)
    background: $icons-hd
    +background-size(image-width(sprite-path($icons)) auto)

@each $icon in sprite_names($icons)
  .icn-#{$icon}
    +sprite-dimensions($icons, $icon)
    background-position: sprite-position($icons, $icon)
    @media (-webkit-min-device-pixel-ratio: 1.5), (min-resolution: 144dpi)
      $offset: nth(sprite-position($icons-hd, $icon), 2) / 2
      background-position: 0 $offset

Thanks nick. I just wrapped up Assembling Sass 2

$icons    : sprite-map("icons/*.png", $layout: smart)
$icons-hd : sprite-map("icons-hd/*.png")

$layout: smart — will save some kb for you. But use it only with non-retina sprite.