This is a reproduction of an article written for the inaugural Cimex magazine in July 2006.
Users who visit sites with devices that support limited or no CSS, or with devices that do not display your content visually will not see your content in the organised columns and colours that the majority do – they will be browsing your site in a single column ordered as your mark-up is. This often means they first receive a long list of nav items, logos and introductory paragraphs when what they really want is the latest article, train time or number of goals Thierry has scored today.
There seems to be a growing trend for developers to include ‘skip to content’ links as a solution to this problem. These links bypass the nav and header elements and move the user straight to the content, but users still have to move around a page instead of being served what they want straight away. This technique also fails to account for other ways in which your data is accessed; search engines indexing your pages may rank prevalent content more highly for example, and they won't use skip links to pursue the content you deem most important on the page. Although I am not an SEO expert I can't believe that important, relevant elements at the top of a page won't have more influence on a search engine in how it interprets the meaning of your site.
There are plenty of CSS techniques that can be used to separate your page structure from appearance—the excellent methods explained at Position Is Everything for creating columns in any order on the canvas, for example. Just remember that the most important column is the one containing what the users came for.