WordPress.org

Install

1. Install in your plugins directory in the usual way and network activate the plugin. There is no need to put it in mu-plugins.
2. Login as a site administrator and go to Super Admin->Sitewide Tags.
   1. "Tags blog" defaults to "tags" but can be anything. This is the blog where your sitewide posts will live. It will be created if it doesn't exist.
   2. Check "Post to main blog" to use your main blog as the tags blog.
   3. "Max posts" defaults to 5000. Older posts will be deleted if this threshold is broken.
   4. Check "Include Pages" to include both posts and pages, handy for making a sitewide search.
   5. "Privacy" defaults to public, pages can be indexed by search engines.
   6. When "Privacy" is not public, check "Non-Public Blogs" to include blogs not indexed by search engines.
   7. Add "Post Meta" custom fields to be copied with posts/pages.
   8. "Populate Posts" allows you to fill in posts from an existing blog.