WordPress 3.5 is scheduled for release in December 2012. The 1st beta was released last week so we can test it out but I don’t recommend using it on any of your live sites.
In additional to the beta WordPress also released the full version of the new Twenty Twelve theme. Twenty Twelve is compatible with the current version of WordPress, 3.4.2, so you can start using it now. I wrote about the features of Twenty Twelve in my previous article.