I just installed Domain Mapping for my WP 3.0 multisite. After uploading to wp-content\plugins, I added define( 'SUNRISE', 'on' ); to wp-config.php.
Then I enabled the plugin for entire network, and enter the IP address for the main site.
Then I logged into my test blog, and tried to enter a domain for it. After clicking Add, the page refreshed but nothing happened. The entered domain value was gone! I checked the wp_domain_map table, it was empty. May I know what did I miss here?