http://www.powerpivotpro.com/

Here are some links I find useful:

• http://technet.microsoft.com/en-us/library/ff607753.aspx
• http://technet.microsoft.com/en-us/library/cc262350.aspx#section1
• http://blogs.msdn.com/b/analysisservices/archive/2010/03/22/powerpivot-component-architecture.aspx
• http://www.sharepointlonghorn.com/Lists/Posts/Post.aspx?ID=13
• http://powerpivotgeek.com/2010/04/22/why-powerpivot-requires-classic-mode-web-applications/
• http://sharepoint.microsoft.com/blogs/GetThePoint/Lists/Posts/Post.aspx?ID=204
• http://asmdx.blogspot.com/