global_terms is not only deprecated, it was never fully functional, and all it did was assign the same category id to identical terms. It didn’t do what you want.
While you can create the same categories on all blogs at the time of creation using something like this plugin:
http://wordpress.org/extend/plugins/wpmu-new-blog-defaults/
the part about making it on the main blog and pumping it out to existing one will take some custom coding.