We tried several times to upgrade our installation of wordPress 3.0 to 3.1. We found several errors after such update. Admin manager too slow, import tool no matter the multimedia library… This is why we have decided to write a script that lets you migrate from WP 3.0 blogs complete (post, users, comments, tags, multimedia).. with top facilities multisite. The script was written very quickly, it may has errors, but can be used to solve the situations. The script is written in classic asp because our WP instalation is over IIS, but can be easily translated into PHP.
if you have WP 3.0 multisite over IIS and PHP 5.2, you can use this script to migrate your blogs (if you have problems with the traditional methods)
Feel free to modify this script or traslate it to PHP, to help to the rest of the WordPress Comunity.