They didn't manage to keep their existing URLs working. E.g., http://docs.heroku.com/background-jobs used to exist (it was cached as a search result by Google), but it now redirects to http://devcenter.heroku.com/background-jobs, which merely says "Page Not Found" (which should be a 404 error but isn't) and only suggests "Loading..." because the author failed to handle progressive enhancement (the menu on the left is non-functioning, for the same reason). I know these guys aren't claiming web development as a competency they sell, but I wouldn't release in a state like that.