Ask HN: What are you doing that your site is so subjectively responsive?
Teach us please... the response time on load is wicked quick. How?
One "trick" that I've found helps to add place-holder gradients for images. So if you have a background image, add a linear-gradient or something as well. That means that there isn't such a jarring transition between the gradient and the image.
But really - keep the JS to the minimum and you'll be good. Also try and avoid using a large CSS "framework" - as that can easily add more bloat. If you start from scratch and only add what you need - keeping it very lean.