I read a post recently where the author mentioned how he disabled registration in CS. Until I work through CS User handling issues and my own approach to site registration (a post-release todo), disabling CS registration sounded like a good idea to me! So I searched high and low in the admin area and sure as heck didn't find an Enable/Disable Registration option. Time to turn it off in the source, deciding on the quick fix of hiding the login/registration hyperlink in the CommunityServer.Controls.DisplayUserWelcome class.
The DisplayUserWelcome class contains a public boolean EnableRegistration property. I haven't seen the ability to set this property from outside of the class, but it does determine the visible property of the login hyperlink. This is set out-of-the-box to true. Change it to false and you've more or less disabled CS registration.
private bool _enableRegistration = false; // DBVT Changed from enableRegistration from true to false
public bool EnableRegistration
{
get{return _enableRegistration;}
set{_enableRegistration = value;}
}