i am using jQuery to dynamically add content
$("#articles").prepend('<article><header><p>info</p><h2>You are using Internet Explorer</h2></header><p>It is recommended that you use a modern browser like Firefox, Chrome or install Google Chrome Frame to experience better performance and advanced HTML5 and CSS3 features.</p></article>');
but the HTML i got was
notice the />
jQuery is using innerHTML, which doesn't always work with HTML5 elements even when the normal ‘shiv’ is in use. You would need another extra workaround hack, eg this.
I really don't think the proposed new HTML5 elements are ready for real-world use. They get you no practical gain yet, aren't even finalised, and cause a bunch of problems (working around which can be fragile and cost performance).
They don't really add anything semantic to your warning markup, and you're only ever showing it to IE anyway—the browser that can handle them least well of all.