I know, SQL Server 2008 R2 was released some time back, but with so much content out there I thought I might simplify it a bit. I've written a complete overview that you can read through in about 10 minutes, and there's a great new whitepaper on one of the main features, PowerPivot. Thought I'd share here:

My article: http://www.informit.com/guides/content.aspx?g=sqlserver&seqNum=359 

PowerPivot Whitepaper: http://whitepapers.zdnet.com/abstract.aspx?docid=1911939&promo=100303