It’s a great idea – don’t listen to them;). It’s the future, and it’s fairly easy to make IE listen to the new tags such as header, section, footer, nav, etc with just a little bit of javascript. I’ve built https://bradyjfrey.com and https://doughahn.net on html5 – and just about every other site in my portfolio still under my control will be html5 in the next few months. My issues with doughhan.net (for those of you with ie6) is simply the CSS3 I want to use. That’s more of an issue I can’t get around!
So to answer some of the comments directly, html5 works in ie8 and under. You can use conditional comments to target them with simply javascript (and by simple, I mean extremely light), such as
<!--[if gte IE 6]>
<script>
document.createElement('header');
document.createElement('footer');
document.createElement('section');
document.createElement('aside');
document.createElement('nav');
document.createElement('article');
document.createElement('time');
document.createElement('mark');
</script>
<![endif]-->
Can also be an external file. While I often don’t advocate javascript solutions, this is a simple one we haven’t had problems with on our marketing testing, and does the job.
