Limitation!
Separation of the footer from the columns will not work satisfactorily. Reason: The body contains a background image and we have no way to accurately, dynamically match a masking image in the footer area.
This Variation
This sparse-content page demonstrates the "lead footer" feature
The floating header is accomplished by masking-divs, not css margining (columns are actually full-height. Their top border is actually the bottom border of the spacer div above them.)