SQL Server 2008 R2 is a minor release and the number of features and enhancements added to the database engine is very limited. The public CTP is available for download at http://technet.microsoft.com/en-us/evalcenter/ee315247.aspx

The following are the main Database Engine Features added in SQL Server 2008 R2 August CTP

1. SQL Server Utility – It allows creating a SQL Server Utility Control Point (UCP) which provides the ability for centralized management and consolidation of SQL Server instances and data-tier applications. SQL Server Management Studio has additional explorer windows ‘Utility Explorer’ and ‘Utility Explorer Content’ for working with Utility Control Point. More information can be found here: http://msdn.microsoft.com/en-us/library/ee210548(SQL.105).aspx
2. Support for more than 64 CPUs - The number of CPU cores that a server can use for database operations has been increased from 64 to 512
3. Unicode Compression - Unicode data that is stored in nvarchar(n) and nchar(n) columns is compressed by using an implementation of the Standard Compression Scheme for Unicode (SCSU) algorithm. A number of bloggers have blogged about this feature.
1. http://sqlblogcasts.com/blogs/simons/archive/2009/08/11/SQL2008-R2---Whats-New---Unicode-Compression.aspx
2. http://sqlblog.com/blogs/aaron_bertrand/archive/2009/08/11/sql-server-2008-r2-a-quick-experiment-in-unicode-compression.aspx
3. http://blogs.msdn.com/sqlserverstorageengine/archive/2009/08/17/unicode-compression-in-sql-server-2008r2.aspx

Did I miss something? Please feel free to add a comment.