I cannot tell you how many times that DBAs have asked me when SQL Server will support Windows Server Core version of the OS. With Server Core, you essentially interact with the OS similar to Linux or Unix with a shell prompt as opposed to the UI-centric model that is familiar to Windows users. This greatly minimizes the server attack surface and also can greatly reduce required patching. These are HUGE advantages for SQL Server DBAs.
SQL Server 2008 R2 does not support installing on Windows Server Core. However, the next version (Denali) of SQL Server will. I just want to point you to a very helpful posting on BOL that gives you guidance on what features of SQL Server will NOT function when installed on Server Core. The link is here. Note that most GUI-centric tools are not available. But the services outside of the core SQL Server engine that most operations require ARE available like Integration Services and Analysis Services.