Google’s created a great demo, 20 Things I Learned About Browsers and the Web, which shows off a lot of great new features, if your browser supports them.
I don’t care much about backwards compatibility or rubbish browsers, so I didn’t look to see how it degrades in IE or anything.
Everybody knows about HTML5 features like video and canvas and so on, but I think that the coolest feature on show here is a little known feature which really helps make web apps viable for me – being able to push history states. Before, ugly hacks had to be used like using a hash symbol to be able to change parts of the URL, but that still didn’t work with the back button and created ugly URLs. Now, using the history.pushState function lets you change the entire URL (apart from the domain name, of course), and each state shows up in the history. You can then catch the event triggered when the user hits the back and forward button, and act accordingly. Now you can have proper history, proper back/forward action, and nice URLs, all without any page reloads! It may seem like a pretty minor feature, but it’s the little things like this that are actually making web apps viable.