Update, December 292015: This blog is now part of WPMU DEV and is about all sorts of things to do with WordPress (not just WordPress MU, which is now called Multisite). Find out more by visiting the WPMU DEV Blog homepage. The content below is preserved for posterity.
Welcome to WPMU.org. a blog dedicated to post news, tutorials, plugins, themes, hacks, tips, etc… related to WordPress MU. What’s WordPress MU?
WordPress Multi-User (WordPress MU) is a fork of WordPress created to allow simultaneous blogs to exist within one installation. WordPress MU makes it possible for any one with a website to host their own blogging community, control and moderate all the blogs from a single dashboard. WordPress MU adds eight new data tables for each blog. (Wikipedia)