CTP5 (also known as November CTP) is now publicly available at http://www.microsoft.com/downloads/details.aspx?familyid=3bf4c5ca-b905-4ebc-8901-1d4c1d1da884&displaylang=en
If you have not it already, please participate in the connect program (https://connect.microsoft.com/SQLServer) to
for the new features and detailed documentation read SQL Server 2008 Books Online.