I have the same problem with this feature I had with Notifo: It sounds awesome, until I try to think where I'd use it. I can't find many uses where it would beat email, even though I use it for some things like HN comment replies, notifications for actions on my web apps and various personal events.

I think the area where notifications are important, but slightly less important than email, yet not so unimportant that you don't want to have a user install another app, is pretty small... Too bad, I very much like the idea of Notifo. When will it stop working? Do you plan on open sourcing any part of it?