jQuery is great, but sometimes on some browsers/devices it can be pretty slow to be implemented and take effect. I'm looking at you iPad/iPhone!
Why is this such a problem?
In the case I came across this was a problem because the jQuery .hide() I was using was acting after the DOM was loaded and the iPad was slow to do this. It was creating a noticable 'pop' when the page was loaded before elements then disappeared. Not the end of the world, but annoying. I asked on stackoverflow and this is the best solution that was provided, not to mention being a bit of genius.
document.documentElement.className = 'js';
It is an incredibly simple and clever solution.