If you use, as Kristine suggests, one blog to store all notifications, then you can modify the sub send_notify routine of the CMS.pm in lib/MT/App to send all notifications from all blogs on an installation to the notification list of a specified blog.
in the sub send_notify routine (line 2595 in MT 2.66), find:
CODE
my $iter = MT::Notification->load_iter({ blog_id => $blog->id });
and change to:
CODE
my $iter = MT::Notification->load_iter({ blog_id => '6' });
Substitute for 6 the number of the blog id where you store your notifications.
Now all the blogs on the installation can send out notifications to emails listed in the notifications list for one of those blogs.
The drawback of this solution is that you can't have a test blog or a blog on the same installation that only sends email notifications to a select list.
(I'd love to see a Test button on the Send a notification form that will only send one email to the author for preview before hitting Send to the whole list. Guess I'll be learning some Perl).
Stacey