If you use sprites... sticking to a grid system makes it so much easier in
SASS...  I didnt do it on the last project I used a big sprite sheet on...
but I will do it on the next one having played with it.

Basically, I made a spritesheet where everything's top-left was on a 20x20
grid corner.  Some things took up multiple grid squares, but the top-left
was always in a grid corner.  Then i just a mixin with variables for the
column and row of the sprite

Then, in SASS/SCSS

$grid_spacing = 20;

@mixin sprite($x, $y) {
  background-image: url(mysprite.png)
  background-position: -#{$x*!grid_spacing} -#{$y*!grid_spacing}
}

.mySpriteButton
 @include sprite(3, 5)
 width: 200px
 height: 50px