Start here: http://www.microsoft.com/sql/2008/learning/whitepapers.mspx.
DataProgrammability http://www.microsoft.com/sql/techinfo/whitepapers/sql_2008_dp.mspx
What'snew for XML in SQL Server 2008 http://www.microsoft.com/sql/techinfo/whitepapers/sql_2008_xml.mspx
Performance: http://www.microsoft.com/sql/techinfo/whitepapers/sql_2008_perfandscale.mspx
Manageabilityhttp://www.microsoft.com/sql/techinfo/whitepapers/sql_2008_manageability.mspx
SQLServer 2008 Reporting Services http://www.microsoft.com/sql/techinfo/whitepapers/sql_2008_ssrs.mspx
