Blog or Website?
WordPress users generally fall into two categories, those who use the hosted version for their websites, and those who use the lightweight Web framework for their blogs or other simpler projects. The WordPress 3.6 release candidate is ready for testing in either of those environments, but some of what's included in the release may not be as relevant for those hosting their websites, for example.
Twenty Thirteen is the name of the default theme, one of the things many websites may opt out of using due to an already existing theme for their site. Twenty Thirteen features quite a different color scheme for those who do intend to use it, but there's also new fonts, scalable icons, and things like native audio and video support that a wider base of sites will definitely be using.
Responsive Theme + Revisions Tool
Features wise, the update getting the most attention seems to be the revisions tool that enables a smoother comparison screen. Switching back and for between multiple revisions shouldn't be as much of a browser killer, for example. Twenty Thirteen is a responsive theme that is a bit different from the 3.5 release because that was built as a mobile first version.
They're both good for mobile devices, and the end result is nearly the same, just with a different approach. In v3.6, Google fonts will be included for the first time, and they are Source Sans for body text and Bitter for headlines. Additionally, open source icons called Genericons have been included in this update.
Another handy update is the inclusion of native support for audio and video. For those who want to include videos, for example, they don't have to embed them from YouTube, instead just adding them right to WordPress pages. There's also been an update on the auto save system, as many people complain about losing posts when they loose Internet connectivity or accidentally refresh a page.
Local storage will be used to help save material between auto saves and manual saves, and a post locking tool will debut as well. That way, it won't be as easy for people to overwrite something one of their colleagues has done. These are good updates, especially for those on the novice end of WordPress usage. Being that this is a release candidate, it's not recommended it be installed on a production website, but WordPress should have a final candidate ready by the end of July.
After that, development of 3.7 will begin, and the post format UI update many hade been clamoring for could crop up then. We often talk about WordPress as it pertains to enterprise usage, and while some of these updates may not matter to those types of users, there's some good things in there to look forward to. Simple things like native video support and revisions control make customization and workflow updates smoother, and that should endear even more people to the ever popular WordPress.