DMNotify- The Latest Iteration of Irssi Notifications
It seems like everybody has their own notification solution for IRC. I've gone through a few over the years, including GMNotify , hodgepodges of Perl and Python scripts unprofessionally cobbled together to leverage Growl notifications, and no notifications at all!
DMNotify is the latest solution, and the best thus far. It uses the Twitter API via Net::Twitter to send DMs on nick highlights and private messages, and you can respond to the last person who notified you. The full README at the GitHub link provides a bit more information.