Microsoft has released the final build of SQL Server 2008 R2 SP1. It includes fixes from SQL Server 2008 R2 RTM Cumulative Updates 1 through 6, and some new features introduced since those cumulative updates.  Release notes for SQL Server 2008 R2 SP1 is available here.

SP1 adds several important new trace events that can make monitoring SSAS much easier.  They are documented in some detail here: http://support.microsoft.com/kb/2458438

More info from Glenn Berry and Aaron Bertrand.