If you're a developer looking to build apps for Windows Server 2008 R2, there are a host of new technologies to consider. Although R2 is an incremental release, it's not your "average R2". Key new feature areas include "many-core" scalability, virtualization, power management, web workloads, and enterprise network solutions. To build the best app, you'll need to learn about select R2 platform technologies and build your own integrated solutions.
Fortunately, Microsoft has completed an online training course aimed specifically at developers looking to leverage all the new feature sweetness in R2. Head over here to get a deeper desciption and access.