HTML5 is not an option
HTML5 is HOT! Developers all over the world are adapting their sites, browsers are catching up, and new fallback solutions are released every day. But many developers misunderstand one thing:
You can’t choose to use HTML5 or not, your site will be parsed as HTML5 no matter what.
The reason is simple, HTML5 is made to be backwards compatible with the current web, so browsers don’t need to keep their current parsers. All of them have soon switched to HTML5 parsers. You want to continue using HTML4? Not possible.
So, go read up on HTML5 if you haven’t already, but don’t think you can keep using HTML4. Your site is being switched over as we speak.