The Great Divide
One of the key points of web standards is the separation of content and presentation. Now, some may call me nit-picky, but if we’re going to separate the two, lets keep them completely separated. I’ve seen too many excellently designed, well known, validated and accessible websites that contain one flaw: There is still presentation information in the content.
When looking through the XHTML of many of these great sites, this is an example of what I see:
<div id="left"> Page Data </div>
This code would be perfectly acceptable if the content of this <div> were describing a political wing, but usually they contain data that is aligned to the left side of the page. This not only goes against the separation of content and presentation, but also, if the presentation of the page would ever be updated, and the data inside of this #left <div> were no longer aligned to the left, this would require updating the XHTML of every page to update the presentation. That’s exactly what web standards are supposed to avoid.
My suggestion is to keep the id of the <div> specific to the data it contains; main-content, supporting-text, navigation, etc.