Since the Microsoft Exchange Conference I've seen several good articles and so on covering Exchange 2013. Here are a few:

• Exchange Server 2013 Moves Toward Simplicity - Blog post discussing the new UI and new features: For the architecture, the big news is that the number of server roles has been reduced from five to two. You'll have to deploy only Mailbox servers and Client Access servers; the functions of the Hub Transport and Unified Messaging servers have been rolled into one or the other of the two remaining....On the management front, Exchange 2013 simplification comes by way of the Exchange Administration Console (EAC), the new web-based GUI for running your Exchange environment. EAC combines and replaces the functionality of Exchange Management Console (EMC), which has been around since Exchange 2000, and Exchange Control Panel (ECP), the web-based management interface introduced in Exchange 2010.
• Exchange 2013 Preview documentation - This is a pre-release set of documentation covering Exchange Server 2013, from Microsoft.
• Microsoft's Exchange Server 2013: What's new - A laundry list of new features, from Mary Jo Foley.
• An evaluation version of the software.