WordPress 4.0 has been released. Upgraded my site without any issues.
Key enhancements include:
Toolbar stays in place as you add content. Allows you to focus on your content.
Seamless Media Embeds
Just placing the link allows you to see the content.
New Plugin Browser
Browse Plugins and Reviews directly in the dashboard.
Media Library Grid
After dragging multiple file, view them in a grid in the dashboard. Video and Audio files playable right there.