Server 2012 is offered in 4 flavors:
- Datacenter ($4,809 retail) allows unlimited VMs on up to two physical processors.
- Standard ($882 retail) allows up to two VMs on up to to physical processors.
- Essentials ($501 retail) replaces SBS, allows up to 25 users, is intended for file or print sharing, Active Directory authentication, DNS, IIS, etc. However, I can tell you that the Office 365 connector is lame, because when users change their password at a workstation it's not replicated up to Office 365 - only console password resets trigger the replication.
- Foundation (OEM only) is for offices of up to 15 people who only need basic file/print services and Active Directory.
This article explains the differences between Essentials & Foundation.
Microsoft is pushing "Server Core" installations and now lets you flip back & forth between core and GUI mode, so that's cool.
By default, all the server installation files get copied to the WinSxS directory. If you're tight on space, you can use PowerShell commands to implement "Features on Demand", which removes the source files of features you're not using.
Server 2012 introduces hardware independent NIC teaming for fault tolerance and higher throughput.
The GUI tool "Server Manager" can export its actions as an XML file that show you the Powershell commands it will be executing (and which can be executed as a batch from the CLI).