I just got finished installing WordPress 2.2. Everything went well except that I got nailed by the wp-cache plugin. I had disabled it before I started the upgrade per the upgrade instructions. When I tried to run the upgrade.php file in the last step of the upgrade procedure, I got a blank screen. After a little debugging I had to manually edit the wp-config.php and remove the line, define('WP_CACHE, true)
line.