The additions or changes in SQL Server 2008 R2 are mostly BI related but there is one I just became aware of that serves a more general purpose but at the same time is fundamental in how the storage engine works related to locking. I won’t rehash (pun intended) what Sunil Agarwal wrote in the below listed blog but in a nut shell they rewrote how the hashing algorithm for calculating lock values and got rid of almost all the potential collisions. While this is one of those features that most people will never hear about we should give Kudos to the team for improving such a fundamental part of the engine.
http://blogs.msdn.com/sqlserverstorageengine/archive/2010/01/18/improvement-in-minimizing-lockhash-key-collisions-in-sql-server-2008r2-and-its-impact-on-concurrency.aspx