Was activate_plugin removed in WP3?

I am trying to programmatically activate plugins on blogs in WP3. BTW I am running this script in a theme template.

It seems that the suggested way to go is: activate_plugin()
E.g. as described here: http://grinninggecko.com/activating-deactivating-wordpress-plugins-programmatically/

Nothing happens for me. Should I be using another function?