optimized grid system from @necolas

lib/preboot.less

@@ -36,6 +36,7 @@
 @gridColumns:       16;
 @gridColumnWidth:   40px;
 @gridGutterWidth:   20px;
+@extraSpace:        40px;
 @siteWidth:         (@gridColumns * @gridColumnWidth) + (@gridGutterWidth * (@gridColumns - 1));
 
 // Color Scheme
@@ -125,21 +126,10 @@
   .clearfix();
 }
 .columns(@columnSpan: 1) {
-  float: left;
   width: (@gridColumnWidth * @columnSpan) + (@gridGutterWidth * (@columnSpan - 1));
-  margin-left: @gridGutterWidth;
-  &:first-child {
-    margin-left: 0;
-  }
-}
-.offsetMath(@extraSpace: 40px) {
-  margin-left: (@gridColumnWidth * @columnOffset) + (@gridGutterWidth * (@columnOffset - 1)) + @extraSpace !important;
 }
 .offset(@columnOffset: 1) {
-  .offsetMath(40px);
-  &:first-child {
-    .offsetMath(20px);
-  }
+  margin-left: (@gridColumnWidth * @columnOffset) + (@gridGutterWidth * (@columnOffset - 1)) + @extraSpace;
 }
 
 // Border Radius

lib/scaffolding.less

@@ -9,6 +9,29 @@
 
 .row {
   .clearfix();
+  margin: 0 -20px;
+
+  // Default columns
+  .span1,
+  .span2,
+  .span3,
+  .span4,
+  .span5,
+  .span6,
+  .span7,
+  .span8,
+  .span9,
+  .span10,
+  .span11,
+  .span12,
+  .span13,
+  .span14,
+  .span15,
+  .span16 {
+    float: left;
+    margin-left: 20px;
+    *display: inline; // IE6 double margin bug fix.
+  }
 
   // Default columns
   .span1     { .columns(1); }