1º - On edit blog configuration, the option "Public" when you set to "No", nothing happen, the blog still be active for user access. (My intend is that this option makes the blog admin access only)
2º - On wp-config.php, these options, "SITE_ID_CURRENT_SITE" and "BLOGID_CURRENT_SITE", doesn't work. The first "SITE..." I don't know exactly what it is. The second "BLOGID...", I tried to change the ID to open another blog when acess the domain, but wpmu just redirect to wp-admin.
These features where tested on a local pure wpmu installation.