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I haven't seen this before posted on this site.
However, I will note that I did change the code in my sites to use by default e-mail notification, which was pretty easy. I've also changed the PM code to send (anonymous) e-mails to the users since none of my clients ever want PMs on their site (although it's another way to bring people back to the site). That information will be posted soon, but I'm still testing and integrating it.
There is the possibility that you could use the SmartMail module from SmartFactory. It seems intriguing but also daunting but may do what you need and want.
If you wanted users to have certain notifications, you could probably add some code in the registration process to enter those into the database, stealing some code from the notifications functionality.