It's the year 2009. Internet Explorer 8 has finally been released, and Firefox is coming up to 3.5. Many of the large browsers are starting to integrate features from CSS3 and HTML 5, or have been doing that for quite a while now. Still, I find myself developing web pages exactly the same way I did back in 2005.
A lot of progress has been made since then, and I think the reason that I haven't started taking advantage of these new possibilities is that it's so hard to know which of the new features that work in all major browsers. Since I'm mostly a backend developer I just don't have the time to keep up these developments anymore. Still, I feel like I'm missing out on a lot of cool stuff that actually would make my life a lot easier.
Thus my question is this: What new browser features (HTML, CSS, JS) are almost universally supported (ignoring IE6 and possibly IE7) and ready for mainstream use, but still mostly unknown?