Other than my comment on the other thread about escape characters, this is a pretty useful plugin and I've confirmed it's worked on a test email to site admins.
There's one problem though. Since we have to use our installation with LDAP user account creation (and thus have to leave users in the system for content integrity, even after they are no longer employees/students), when I load a list from a user role, there is no way to exclude any users. In my case, this will always send to at least one or two, if not many, invalid email addresses.
What would be ideal would be to add a checkbox beside each name in the generated list, whereby checking it would exclude that email address (or check them all by default and deselect might be more intuitive).
Also maybe just update the plugin to confirm it's been tested on WP 3.5.
Nice work though.