The W3C page on why you should do this: http://www.w3.org/TR/WCAG20-TECHS/G140
The The Universal Usability page: http://universalusability.com/access_by_design/document_structure/separate.html
Wikipedia has an article at: http://en.wikipedia.org/wiki/Separation_of_presentation_and_content
CSS Zen Garden shows how the look of a page can change with the same content : http://www.csszengarden.com/
Ohio LinuxFest is September 28-30 in Columbus, Ohio. Go to https://ohiolinux.org/ for more information.
My web site is at hhttp://www.ahuka.com/.
Remember to support free software!