Semantically speaking…
Still using div id's like "header", "footer", "left_bar", "right_bar", "sidebar", and so on? Then, you need to read on.
Division ID's like the ones listed above are about as dead as using table layouts. I can say it in a nutshell, but it doesn't seem like designers really understand what's going on...
SEPARATE STRUCTURE FROM PRESENTATION
In other words, if you're naming classes and id's with respect to how they appear on the screen, you're completely missing the point. Assigning the "header" ID to a division tag tells you almost nothing about what's in it. If I had to guess, the tag probably contains the title and maybe a slogan or a byline, but you never know. Some people put navigation lists in the header. (Some people put way too much in the header.) So, the word "header" doesn't nearly describe what might end up in there.
Content is king
So, what does this mean for your average xhtml enthusiast? It means you must have content before you can effectively design the markup. That's the main problem with most clients these days. They usually don't give designers content. Lorem ipsum text can only go so far.
So... what if you don't have content?
Write some fake content that is more real. It's probably best to start writing the content in your favorite word processor. The point of doing this is that you don't really start to notice patterns in your content writing until you have more than one page. Maybe the original wire frames were for a 3-column layout, but after receiving the real content, it might be beneficial to switch to a 2-column layout.
Once you have your content, you can identify the patterns, and define your markup naming schemes. ALL of this should be done before you even begin to think of layout.
