I think that notifications in app and on the live tile are great ideas.
On the other hand, Twitter, Tumblr, and YouTube all send me an email when someone follows or subscribes to me, comments on my post, etc. so I don't think that email notifications are too far out of line. They have the benefit of getting ahold of me even when the device I'm currently using doesn't have the service's app installed on it.
Perhaps YouTube moving toward Google Plus notifications for many things is a point in Joscelin's favor, though.