a gradient mix-in for LESS (tested with dotLESS, but may work with LESS.js)

_gradient.less

.gradient(@from:#fff, @to:#fff, @fallback:@from) {
  /* https://github.com/jamesfoster/dotless/commit/4004eff3cab321e31f43d052e35b5538f19443f7 */

  @ffgradient: "-moz-linear-gradient(top, {0}, {1}) no-repeat scroll 0 0 transparent";
  @wkgradient: "-webkit-gradient(linear,left top,left bottom,color-stop(0, {0}),color-stop(1, {1}))  no-repeat scroll 0 0 transparent";
  @iegradient: "progid:DXImageTransform.Microsoft.gradient(startColorstr='{0}', endColorstr='{1}')";
  @ie8gradient: "\"progid:DXImageTransform.Microsoft.gradient(startColorstr='{0}', endColorstr='{1}')\"";

  background: @fallback;                              /* for non-css3 browsers */
  background: formatstring(@ffgradient, @from, @to);  /* FF3.6+ */
  background: formatstring(@wkgradient, @from, @to);  /* Saf4+, Chrome */
  filter: formatstring(@iegradient, @from, @to);      /* IE6,IE7 */
  -ms-filter: formatstring(@ie8gradient, @from, @to); /* IE8 */ 
}


/* usage */

.some-selector {
  .gradient(#454545, #000, #454545);
}

What about support for multi-stop gradients ? like
background-image: -o-linear-gradient(-45deg, rgba(255, 255, 255, 0.15) 25%, transparent 25%, transparent 50%, rgba(255, 255, 255, 0.15) 50%, rgba(255, 255, 255, 0.15) 75%, transparent 75%, transparent);