CSS calc appears to be supported in the plans for both firefox and IE new releases. Nothing is yet known about Webkit, Chrome and Opera support time frames.
Where this is needed is in floating design styles which have a fixed width element that must be included. So the last column needs to take all the space that is left over; as it stands now the floating element only takes up the space it needs or is given. The background of the element does not extend all the way to the side. The work around is using layers.