I ran across this document a couple of weeks back that illustrates how Integration flows work within the SharePoint, Exchange, Lync Server, and Office Web Apps products. Great for quick refresher on how these systems integrate together within Office 15.
Illustrations for cross-server features: This multi-tab file includes descriptions and architecture illustrations for features that work across Microsoft Office server products including:
Office Web Apps Server
Server-to-Server Authentication (OAuth)
High-Resolution User Photos
Unified Contact Store
Exchange Task Synchronization