The SQL Server Technical article entitled Resource Governor in SQL Server 2012 has just been published.
The article focuses on the SQL Server 2012 enhancements to the Resource Governor which reflect a growing need for centrally managed database services to support isolated workloads in multitenant environments.
This document describes the enhancements and why they were added. It includes a self-contained walk through that you can try for yourself in order to gain familiarity with the new features.
If you're not familiar with the SQL Server Resource Governor (which was introduced in SQL Server 2008), start with a comphrehensive white paper called Using the Resource Governor and then come back to Resource Governor in SQL Server 2012 to see what's new.