make sure you have updated your wp-config file, it differs from version in 2.9.2 calling wp-settings.php an include, if your config file is not updated to reflect the new 3.0 changes WP-super cache will refuse to move from the WP_CACHE needs to be enabled message..
if you just move your db settings into the wp-config-sample.php and then rename it wp-config.php you should be good to go…
