Suzi's Media Query mixins

suzi-mq.scss

@mixin media-query($value, $ltie9: true, $operator: $min, $px: false) {
	@if ($operator == $max and $value < $site-width) {
		// Do nothing
	}
	@else {
		@if ($ltie9 == true) {
			.ltie9 & {
				@content;
			}
		}
	}
	
	@if ($px == false) {
		@media (#{$operator} #{em($value)}) {
			@content;
		}
	}
	@else {
		@media (#{$operator} #{strip-units($value)}px) {
			@content;
		}
	}
}

@mixin media-query-and($first-value, $second-value, $ltie9: true, $first-operator: $min, $second-operator: $max, $px: false) {
	@if ($ltie9 == true and ($second-value >= $site-width)) {
		.ltie9 & {
			@content;
		}
	}
	
	@if ($px == false) {
		@media (#{$first-operator} #{em($first-value)}) and (#{$second-operator} #{em($second-value)}) {
			@content;
		}
	}
	@else {
		@media (#{$first-operator} #{strip-units($first-value)}) and (#{$second-operator} #{strip-units($second-value)}) {
			@content;
		}
	}
}

@mixin media-query-retina {
	@media (-webkit-min-device-pixel-ratio: 2), (min-resolution: 192dpi), (min-resolution: 2dppx) {
		@content;
	}
}

Here's a simplified (!) version of what I'm using. Note that two separate css files are output, each of them without duplicate rules. Also means you can use +respond-to(obsolete) to quarantine IE hacks to the oldIE css file.

$bp05: 28em
$bp1: 42em
$bp2: 56em

=respond-to( $media )
  @if $ie
    @if $media != smallest
      @if $media != onlylap
        @if $media != hires
          @content

  @else if $media == onlylap
    @media only screen and (min-width: $bp1) and (max-width: $bp2)
      @content
  @else if $media == widepalm
    @media only screen and (min-width: $bp05)
      @content
  @else if $media == lap
    @media only screen and (min-width: $bp1)
      @content
  @else if $media == desk
    @media only screen and (min-width: $bp2)
      @content
  @else if $media == smallest
    @media only screen and (max-width: $bp1 - .001em)
      @content
  @else if $media == hires
    @media only screen and (-webkit-min-device-pixel-ratio: 1.5), only screen and (min-resolution: 144dpi)
      @content