Somewhat overshadowed, for obvious reasons, by the big RTM release of SQL Server 2012 was the RTM release of PowerPivot 2012.  You can go download the much improved version of PowerPivot for Excel here.

http://www.microsoft.com/download/en/details.aspx?id=29074

To give you a fair warning there are some prerequisites to installing that were not required in the previous version of PowerPivot that you can find on the download site:

• Install .NET Framework 4.0 and Visual Studio 2010 Tools for Office Runtime.
• If you are running Windows Vista or Windows Server 2008, install the platform update.
• Install Microsoft® Office 2010.
• Install PowerPivot for Microsoft Excel

Also, here’s a few post I wrote several months ago that will help you learn the latest release:

• PowerPivot – Creating KPIs
• PowerPivot – Perspectives
• PowerPivot – Creating Hierarchies
• PowerPivot – Commonly Used DAX Expressions