Although there isn't much difference from an end-user's perspective, some issues I had with the site's admin menus have gone away in the July CTP. Those menus are built with nested Atlas Control Toolkit components of some complexity (such as ReorderLists inside UpdatePanels inside CollapsiblePanels inside UpdatePanels). Here is an image of the site config menu and another image showing the interface for editing and sorting mosaics.
The Atlas Control Toolkit, a great library of useful Atlas-enabled controls built on top of the core Atlas runtime, was also updated in July. It's being built collaboratively with the broader .NET developer community as a shared-source project. The July update is particuarly cool because, as Scott Guthrie explains, the Control Toolkit now includes community-driven content.
My upgrade to the July CTP went without a hitch. With so much community support and demo material available, it's highly recommended to web developers who want to rapidly enrich the user experience of their sites.