1. Database Availability Groups – Database Availability Groups combine CCR and SCR functionality to provide a single solution for both scenarios.  What happens here is that you install a DAG member and it behind the scenes installs Failover Clustering making the High Availability deployment more intuitive for the administrator.  There was one scenario we ran into here where we had two source CCR Clusters wanting to replicate to the same target SCR Standby.  The problem here is that when you recoverCMS on the SCR Standby, the replication fails with the other source CCR that was still working becuase the target SCR server can only ever have 1 CMS.  DAGs fix that issue.
  2. Outlook Web Access Features – There are quite a few new features with OWA.  Some features I really like are:
    • Side-by-side comparison of calendars
    • Ability to attach messages to messages
    • Integration with Communicator including presence, chat, and a contact list
    • Conversation View
    • Support for multiple browsers such as Firefox and Safari
  3.  Unified Messaging Features – There are quite a few new features with UM.  Some features I really like are:
    • Message Waiting Indicator
    • Voicemail Preview – This is essentially a speech to text that will display the text in your e-mail message to get a preview of what the voice mail includes
    • Personal auto attendants
    • Protected Voice Mail – Ability to track and restrict where voice mails can go
  4. Store Functionality  – There are a ton of new features for UM.  Some important things to note:
    • No more Storage Groups
    • Mailboxes are no longer connected to the server object in which the schema has been flattened to allow for this
    • I/O Improvements including JBOD support and better support for SATA disks
    • Being able to run on cheap disks (SATA) and have a backupless organization by having multiple copies stored on DAG members.
  5. Administration  – There are a ton of additions/enhancements to administration.  Some important things to note:
    • Role Based Access Control (RBAC) – Allows you to create granular permissions on custom groups that you create. This essentially replaces the administration model in Exchange 2007.  For example, if you want a help desk group that has access to specific pieces of functionality within Exchange, you can do so.
    • Exchange Control Panel – Ties into RBAC and shows/hides features you are not given access to.
    • Audit Logging
  6. Other
    • Multi-Mailbox Search
    • Text Messaging Integration (SMS)
    • Moderation and approval of distribution group submissions
    • Mail Tips – Will notify an Outlook user of an impeding error before it happens so the user doesn’t get a confusing NDR.  For example, if your message size limit is 10MB and the user tries sending a 15MB message, Outlook will notify the user before the user tries to send out the e-mail saving Exchange resources and making the failure experience more intuitive for the end user.

There’s definitely quite a bit more in which you can start reading here.  I’ll mostly update this post here and there so be sure to check back.  You can definitely expect me to start creating new content around Exchange 2010 in the near future