Hi,
  You are not speaking about security here but it's
a very important
 subject. With what you described any user could be able to register
 any macro usable by anyone in which he can do whatever he want with
 the rigths of the user of the macro.
 The best would be that a macro created by a user is usable only by
 himself until this macro is promoted as standard macro in some admin
 UI. But this mean we can't just register the macro as standard
 component when it's saved, we would need at least the standard list
 and the users list of macros in the DefaultMacroManager or support
 this standard component VS users component in a more generic way like
 the component realms suggested by Vincent.
 Maybe the first step only register the macro if the users which
 modified it has programming rights.
 
Yes, sounds good as a start.
Thanks.
- Asiri