An comprehensive whitepaper regarding the installation and deployment of PowerPivot has been recently released by the SQL CAT Team. It can be accessed from the below site:

http://sqlcat.com/whitepapers/archive/2010/04/14/microsoft-sql-server-2008-r2-powerpivot-planning-and-deployment.aspx

Direct link to whitepaper: Microsoft SQL Server PowerPivot Planning and Deployment

Summary: Microsoft® SQL Server® PowerPivot technology redefines how IT departments deliver and succeed with BI. This technology gives users the power to drill into any aspect of their business and compress decision cycles to gain deeper insight, and it enables them to share their findings with others effortlessly and securely. At the same time, the IT department gains effective new management tools to increase operational efficiency in a Microsoft SharePoint® Server 2010 farm environment.Establishing a PowerPivot environment requires deploying the PowerPivot for Excel® 2010 add-in on workstations running Microsoft Office 2010 and PowerPivot for SharePoint on SharePoint application servers. Those tasks are independent of each other, but planning and coordination are required to ensure the overall success of the deployment efforts.