No I didn't go as far as using any HTML5 elements such as <header> or <footer>, although my pages contained <div> elements with similar ID's.
What I mean is that I had a bunch of XHTML 1.0 Strict pages (that all validated nicely) and I simply changed the DOCTYPE declaration at the top of the pages from this:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
...to this:
<!DOCTYPE HTML>
I'm of the belief that it's best to make your HTML code as simple and short as possible, so when it came to changing the DOCTYPE declaration as shown above, I didn't have any XHTML in my existing pages that wouldn't validate if it were used in an HTML5 page.
So simply by changing the DOCTYPE, I've effectively converted my pages to HTML5. They don't use any of the fancy HTML5 features (yet) but I've laid the groundwork in preparation. Plus there's the added bonus that because the HTML hasn't changed at all (because I had nothing in there that doesn't validate with HTML5) I know that my pages still look the same as they previously did in all browsers.
Whether or not other people can do the same thing depends on how complicated their HTML code is to begin with, and how much of it won't validate with HTML5. As I say, my code is as simple as I could make it, and so I was lucky in that when I changed the DOCTYPE, it still validated, even as HTML5.
