Just wanted to let you know that I've installed this useful plugin in my 3.5.2 blog at: http://my2cents.gawaher.com and it is working flawlessly. I was suspicious because it was not updated since 2010, but installing it was a piece of cake. You can try it in my blog if you want, but the reply you'll get will be in Arabic! (one can easily customize the email it sends).
What's beautiful about this excellent plugin, is that it sends emails to non-registered users, based on the email they leave when commenting at your blog.