WPMU: can I share users and categories across blogs? WordPress

Cristian Antohe answers:

A user can have access to multiple sites. You will have to go into each blog back end logged in as the super admin, select Site Admin -> User, Edit the user name you want and then select that particular role you want it to have the the current blog.

As for the category and keyword part of things I think the easiest way to do it would be using the RSS from the original category / keyword (something like: http://www.cozmoslabs.com/category/thematic/feed/rss/ ) and create a custom page template that lists that rss into all the other WPMU sites. Another way to do it would be to create a query inside that will get the posts from the database directly (using wp functions of course :))

Arania Jain answers:

Hello,

All the users on your WP MU site have Subscriber level access on to all blogs on the site (i.e. they can comment on all blogs with single login). You can optionally change their permissions on a per blog level through the blog admin interface logged in as the site admin.

For the tags (keywords) you can use the [[LINK href="http://wordpress.org/extend/plugins/wordpress-mu-sitewide-tags/"]]wp-mu-sitewide-tags plugin[[/LINK]]

Lastly, for the site wide categories, you can do this - [[LINK href="http://codex.wordpress.org/WPMU_Site_Wide_Categories"]]http://codex.wordpress.org/WPMU_Site_Wide_Categories[[/LINK]] - Although it's for the older version of WP MU.

For your reference, here are links to two other plugins which can be used to create default categories for the blog at the time of blog creation.
1. [[LINK href="http://wordpress.org/extend/plugins/wpmu-new-blog-defaults/"]]http://wordpress.org/extend/plugins/wpmu-new-blog-defaults/[[/LINK]]

2. [[LINK href="http://natureofmind.org/30/default-categories-for-new-blogs/"]]http://natureofmind.org/30/default-categories-for-new-blogs/[[/LINK]]

Hope this helps in solving your problem.

Regards,
Arania