I've just upgraded to WordPress 3.5 and following this, I have updated the cbnet Multi Author Comment Notification to the latest version (v 2.0) on my dev site. When it tried to activate it, the following error was shown:
Fatal error: Cannot redeclare wp_notify_postauthor() (previously declared in ....../wp-includes/pluggable.php:988) in ....../wp-content/plugins/cbnet-multi-author-comment-notification/pluggable.php on line 135
(Note: I've edited the full path (replacing it with ......) so it only includes the relevant bit).
Each time I try to activate the plugin, I get the same fatal error. I've deleted the plugin and reinstalled it but still get the same problem.
The old version of the plugin seems to be working under WordPress 3.5 on my live site, so it's an issue with the major re-write in 2.0.