The next version of SQL Server (code name Denali) will include support for Windows Server 2008 R2 Server Core: http://blogs.msdn.com/b/nikosan/archive/2010/11/11/future-sql-server-edition-denali.aspx. I'm sure more information will be posted as SQL Server gets closer to release.
Exchange is the most common platform of Microsoft. For performance reasons, it should be ported on Server Core first.
Yes Exchange 2010 or 2007 cannot be installed on server core neither supported.
Core requires less memory, no GUI best suited for it.
SQL Server Denali CTP3 on Windows 2008 R2 Server Core