Your WordPress MU comes with two default themes activated. Your type of WPMU installation determines how many other themes are included.
‘Out-of-the-box’ wp.mu, where the installation of WordPress MU is done for you, includes over 100 premium themes installed. When you install your own WordPress MU it includes only two themes and it’s necessary to extend these by installing extra themes that have been customized for WPMU compatibility.
All premium themes have been completely tested and customized to work with WPMU. This means you’re not going to have to upload a single file, edit a single line of html, php or CSS or concern yourself with bugs or issues; they’re ready to use as is!
WPMU-Dixi, WPMU-nelo and WPMU-triden are the most customizable of these themes:
1. WPMU-Dixi includes optional RSS feed for up to 4 feeds on the front page.
2. WPMU-nelo: see this theme in use on Sample Academic blog
3. WPMU-triden includes the option of a custom image gallery – see this theme in use on Sample Student portfolio
If you are considering installing additional themes you need to realize not all themes that work on WordPress work well with WPMU. Most themes in the WordPress Theme Directory won’t work on WPMU.
As Site Admin you have the choice to enable:
1. All themes site wide so that all users can choose from the entire selection of themes
2. Limit number of themes site wide and enable specific themes on a blog by blog basis only