Re: bbpress and memcache?
You can setup a new memcached instance to avoid clashes with wordpress, but if you are sharing user tables then it shouldn’t matter.
If you add another memcached instance on a different port you can point bbPress to it by adding this to bb-config.php (default IP and port shown here)…
$memcached_servers = array( 'default' => array( '127.0.0.1:11211' ) );