As promised, I am proceeding with Exchange 2010 features and, this week, I went to Chris Mayo's blog (referenced at the bottom) and found the following webcasts regarding EWS, Exchange Web Services, including 4 Deep Dive sessions.

But first, "what is EWS" ?

Exchange Web Services gives you programmatic access to the information and business logic in Exchange 2010.  If you think about all the stuff you do in Outlook 2007 to manage your daily life (mail to communicate with friends and coworkers, calendar items to manage your day and tasks to track the things that you need to get done), all that information and business logic (think free/busy when scheduling a meeting) is provided by Exchange and accessible via the Exchange Web Services Managed API.

Check out the following web casts to learn more. 

10/13/2009 - Exchange Server 2010 Development (Part 1 of 6): Migrating Applications to Exchange Web Services

10/14/2009 - Exchange Server 2010 Development (Part 2 of 6): A Deep Dive into Using Autodiscover Service in Exchange Web Services

10/15/2009 - Exchange Server 2010 Development (Part 3 of 6): A Deep Dive into Impersonation and Delegation in Exchange Web Services

10/20/2009 - Exchange Server 2010 Development (Part 4 of 6): A Deep Dive into Exchange Web Services Notifications (Push/Pull)

10/21/2009 - Exchange Server 2010 Development (Part 5 of 6): A Deep Dive into the Exchange Web Services Managed API

10/22/2009 - Exchange Server 2010 Development (Part 6 of 6): Best Practices for Building Scalable Exchange Server Applications

Source: Chris Mayo's Blog - Unified Communications Development : Exchange 2010 and Exchange Web Services - What’s New Webcasts
http://blogs.msdn.com/cmayo/archive/2009/10/07/exchange-2010-and-exchange-web-services-what-s-new-webcasts.aspx