Few days ago, WordPress MU 1.3 was released for public. This latest release is a sync of WordPress 2.3.1. So, many new features offered by WordPress 2.3.1 will be also available in WordPress MU environment. Great!
Here are some features offered by this release:

• Better admin controls for the signup page. It can be disabled in various ways.
• Upload space functions have been fixed.
• The signup form is now hidden from search engines which will help avoid certain types of spamming.
• Profile page now allows you to select your primary blog.
• Database tables are now UTF-8 from the start.
• If you’re using virtual hosts, the main blog doesn’t live at /blog/ any more.
• The WordPress importer now assigns posts to other users on a blog.
• A taxonomy sync script is included in mu-plugins but commented out. It hasn’t been tested much but if your site has many hundreds of blogs it might be worth spending some time on a test server. Replicate normal traffic patterns and see if the server can cope with the upgrade process. If not, then look at the sync script, uncomment it and iterate over all your blogs with a script.

Those features gives me reason to upgrade WordPress MU-powered sites I maintain. If you follow my blog, you probably had heard that all Asia Blogging Network channel domains (14 domains!) uses WordPress MU. For the first step, I think I will dig the features first, checking the template tags (I hope all current template tags are compatible with WPMU latest version), checking plugin compability, and finally… upgrading. I hope I can finish all the work within this week.