Recently it has become all the rage to use AJAX/HTML5 for navigation: instead of letting the browser fetch a page from scratch, a part (or all the content - I am looking at you, pjax) is fetched via AJAX and the URL is manipulated via the new pushState functionality introduced in HTML5.
If github can't, chances are you can't either. So checkout out why you should not do it.
I would love to be proven wrong. Leave a comment.
Update: Oh my gawd, even the new bobdylan.com uses this horrible abomination of a bad idea!