A simple way to include both low-res and hi-res graphics for iOS/Desktop/etc.

_sass-retina.sass

@mixin hires-graphic($file, $type, $width, $height)
  $file-name: $file + "." + $type
  $retina-name: $file + "-retina." + $type

  @media (-webkit-min-device-pixel-ratio: 2)
    &
      background-image: image-url($retina-name)
      -webkit-background-size: $width $height

example.sass

.facebook
  display: block
  width: 20px
  height: 20px
  background-repeat: no-repeat
  @include hires-graphic('icon-facebook', 'png', 20px, 20px)