After doing front-end development for 10 years, I have come to the conclusion that 97.3% of all my annoyances with CSS would disappear if IE and Opera adopted the Flexible Box Model (http://www.w3.org/TR/css3-flexbox/): vertical centering, scaling based on available space, constraints-based scaling, etc.

This is basic layout behaviours that I keep spending hours implementing in JS, which is slow and brittle, because you need fallbacks, etc.