Cookies have been around for quite some time (the ones in browsers, not chocolate chip). HTML5 local storage takes this one step further. Instead of being limited to 4096 bytes of information, we now have a theoretical limit of 5 - 10 MB of local storage. Of course, that means that malicious individuals have a lot more information they can store on unsuspecting individuals who visit malicious websites in the future (potentially). I know safeguards are present, but I was once "paid to be paranoid."
I am creating a little local storage and accessing it with the following buttons. Don't forget to view the source code. If your browser supports HTML5, also inspect the element. the example below comes from: http://webdevlife.com/getting-started-with-localstorage-in-html5/ (and has been modified).