I prepared a set of slides for my Multisite Q&A at the WordPress Winnipeg meetup, in case there weren't enough Qs. I ended up not needing them (though a couple of them came in handy when answering the questions). Anyway, here's the slideshow, if you're interested.

1. WordPress Multisite Q&A
Patrick Johanneson
Web Coordinator, Brandon University

2. Why Multisite?
● You want multiple separate sites running off
a single WordPress installation (eg, client
sites for a WP shop, or you want to be a blog
baron)
● You want many related sub­sites maintained
by different users (in my case, University
sites)

3. Why not Multisite?
● You just want to have many pages with different
looks—you can probably do this with a combination
of a theme, plugins, and possibly custom post types
● You want an interconnected set of pages—
interconnectivity isn't a hallmark of MS (though it
can be achieved without too much difficulty)
● You want different users to see/edit different
content—WP's user levels may be all you need

4. How do I install Multisite?
● Detailed instructions are available on the
Codex page "Create a Network"—
http://codex.wordpress.org/Create_A_Network
Follow them. This is a quick overview of the
process.

5. Multisite Installation
● Prepare your WordPress installation
● Back up files & database
● Ensure that Pretty Permalinks work
● Turn off any plugins
● Add the following to wp-config.php:
/* Multisite */
define( 'WP_ALLOW_MULTISITE', true );

6. Multisite Installation (2)

7. Multisite Installation (3)

8. Super Admins
● Multisite adds a new layer of administrative
user to WordPress's collection
● Super Admins are able to administer global
settings for the entire network
● Theme & plugin installation
● User administration
● WordPress updates (core, plugins, themes)

9. Themes & plugins in Multisite
● Themes must be enabled for a site (or globally)
before the sites' administrators can select them
● Plugins may be activated by individual sites'
administrators, but they may also be network
activated (ie, enabled globally)
● You may choose to allow site admins to add plugins
to their sites
● Both must be updated in the Network Admin view
by a Super Admin

10. Multisite users
● Once a user is added to one site in a Multisite
network, she may be added to other sites in the
same network
● Users' profiles, passwords, etc are the same on all
the sites they edit
● Users may have different privileges on different
sites (eg, Editor on Site A, Administrator on B,
Author on C & D, no privs on E­Z)

11. Some handy plugins
● Network Plugin Auditor
Shows what sites your plugins are activated on
● MU Domain Mapping
Allows you to have multiple domain names (eg,
example.com, smurfy.com, warthogs.ca) running on
a subdomain site
● Networks for WordPress
Allows multiple networks from a single WP
installation

12. Developing for Multisite
● Always restore_current_blog() after
switch_to_blog()
● There are tons of handy functions: check the
Codex and/or wpseek.com (or your favourite
WP–related site) to find the one you need
● is_multisite()
● wp_get_sites()
● is_main_site()
● get_current_site()

13. References
● The Codex—http://codex.wordpress.org
● Before You Create a Network
● Creating a Network
● Function Reference—especially the Multisite
Functions section
● wpseek.com
● wordpress.stackexchange.com—Got
questions? They got answers.

14. Thanks!