PowerPivot on SharePoint 2010 are useful, but SharePoint must be "Server Farm" version. because standalone version couldn't add PowerPivot farm into SP2010.
view document : PowerPivot for SharePoint – Existing Farm Installation
and this : http://msdn.microsoft.com/en-us/library/ee210616.aspx
and this: http://msdn.microsoft.com/en-us/library/ee210708.aspx
7/20 update. I created a document to know how to use Powerpivot and how to post pivot chart on SharePoint, document on Google Drive. Name is "Power Pivot for Excel and SharePoint"
