Microsoft PowerPivot for Microsoft Excel 2010 provides ground-breaking technology, such as fast manipulation of large data sets (often millions of rows), streamlined integration of data, and the ability to effortlessly share your analysis through Microsoft SharePoint 2010.
I have recently started to work with SQL Server 2008 R2 and find the product extremely stable and feature complete. I have installed PowerPivot and I am finding it to be also integrating very well with the product. I recently did one presentations using this two technology and worked very well.
Let me know if you are using PowerPivot for your power BI users. If you are using what is their experience?
Reference: Pinal Dave (http://blog.SQLAuthority.com)