Are the two fully integrated? Just users or functions as well?
With MU 1.2.4/bbpress 0.8.3 I am able to put this in the end of the wp-config.php file just fine.
// Include bbPress functions
define('WP_BB', true); // Avoid duplicate functions
require_once( ABSPATH . '../forums/bb-load.php');
With MU 1.3/bbpress 0.8.3 having that yields a Cannot redeclare update_user_status error.
