@subotnick : I expanded Semantic.gs to allow for fluid columns without margins - either on both sides, just left or just right.

flushcolumns.less

.columnflush(@x,@columns:@columns) {
    display: inline;
    float: left;
    width: @total-width*((((@gutter-width+@column-width)*@x)) / @gridsystem-width);
}

.columnflushleft(@x,@columns:@columns) {
    display: inline;
    float: left;
    width: @total-width*((((@gutter-width+@column-width)*@x)-(@gutter-width*.5)) / @gridsystem-width);
    margin: 0 @total-width*((@gutter-width*.5)/@gridsystem-width) 0 0;
}

.columnflushright(@x,@columns:@columns) {
    display: inline;
    float: left;
    width: @total-width*((((@gutter-width+@column-width)*@x)-(@gutter-width*.5)) / @gridsystem-width);
    margin: 0 0 0 @total-width*((@gutter-width*.5)/@gridsystem-width);
}