Using network virtualization, you can build multiple logical network topologies on top of your physical network infrastructure and parse them out among users and workloads, allowing you to move around network resources and workloads without having to change anything at the physical level -- and without users being the wiser or bumping into one another.
A little further into the future, you can see where this is headed: Complex network capabilities move into virt-space while the network physical layer moves toward an ever flatter design intended merely to provide capacity. That might frighten network administrators today, but as long as you stay current with network virtualization your job will just move into virt-space along with your network.
At the heart of Windows Server 2012's network virtualization is the new Hyper-V Extensible Switch. This looks like a very slick piece of code, but of course it's hot off the forge: You'll want to make sure it stands up to your network requirements before designing anything that needs the v-switch as a dependency.
In a smart move, Microsoft has made the v-switch an open platform based on the Network Device Interface Specification (NDIS), which means third-party network vendors can design plug-ins for value-add features. Expect to see a few of these available at Windows Server 2012's ship date, though I bet the bulk will come out some months after that. Such extensions will allow you to build v-switch-based network infrastructure for specific tasks such as firewall and intrusion detection, packet filtering and inspection, and more.
The many new storage-oriented features Microsoft has built into Windows Server 2012 should also turn your head. There are too many to cover in-depth in this space, but make sure to evaluate Virtual Machine Storage Migration, updated controls for Windows Storage Management, thin provisioning support, and the new Storage Spaces, to name a few.
You can sum up Storage Spaces as the ability to group your storage resources into logical pools. Allocate one disk, pieces of one disk, or multiple disks to give users and workloads consolidated logical storage ... well, spaces. This feature is designed to work with Windows Server 2012's failover clustering, so you can keep storage pools running behind server clusters without as much concern for physical hardware.
Roll-your-own storage systems This bleeds directly into another subset of storage features you'll want to explore deeply: better DIY SANs, or the ability to provide high-availability and high-performance storage on commodity hardware. Microsoft has done quite a bit of work on giving Windows Server 2012 the ability to act as an integrated front-end management interface for third-party storage solutions, while also giving storage managers even more tools to roll their own storage solutions across a broader variety of hardware.