Version 2 of PowerPivot (download) is being made available with SQL Server 2012.  There are many new features, and my top 5 are:

Diagram View – Instead of looking at the defined relationships in a list format, v2 allows you to view the relationships in a diagram.  This makes it much easier to view how all the data fits together

KPIs – You can now create Key Performance Indicators

Hierarchies – There is now functionality to model parent-child relationships along with a PATH function to display the path of a parent-child relationship in a delimited format

Perspectives – You can define subsets of a model to provide a simplified view for the end-user (same as in SSAS)

Sort by Other Column – Allows for sorting one column by another column within the same table.  For example, the month name column can be sorted by the month number column

Note that PowerPivot supports files up to 2GB in size (after compression).  This is an “artificial” restriction that allows it to be uploaded into SharePoint.  The 64-bit version of PowerPivot enables you to work with up to 4GB of data in memory, and the 32-bit version enables you to work with up to 2GB of data in memory (but realistically only 500-700MB, see How much data can I load into PowerPivot?).  And because of compression, PowerPivot can fit an additional 1-10x times the size of the database into memory, so the 64-bit version can fit a 4GB-40GB database into memory.  Typical compression runs about 2:1.

More info:

SQL Server 2012 PowerView and PowerPivot v2

What’s new in PowerPivot for Excel with SQL Server Code Name “Denali” CTP3

What’s New in PowerPivot

Video What’s New in Microsoft SQL Server Code-Named “Denali” for SQL Server Analysis Services and PowerPivot

Microsoft PowerPivot Code-Named “Denali” CTP3 Release Notes

Using PerformancePoint Services (PPS) with PowerPivot SQL Server 2012 RC0

Using the Calculation Area and DAX in SQL Server 2012