Windows Server has had the ability to install only the core features, it is not something that I have done as I have not found it useful.
With the release of Server 2012, I can see the value in installing core only. The first server i would install core only is on Domain Controllers. Why? I have seen time and time again Administrators browse from Domain Controllers and cause them to get spy ware and malware. I have also seen people use them as a default for test programs. This will prevent this nonsense.
Windows Server 2012 has a great management console that makes remote management of servers very easy and is very useful. You can also configure some basic features on the server core by running a command called sconfig.exe.
I also like the fact that the GUI overhead is removed and how quickly the server boots.
I believe Microsoft has finally gotten server core 2012 right and it will be something more and more people are going to use.