It would be great if Duolingo had in-site notifications like Facebook has. I don't care much for receiving notifications via email, but if I disable them I don't get to know when people respond to my subscribed threads, suggest corrections to my translations and so on. I think that would be a very useful feature. Any chance of having it implemented? :)
The stream kind of already does this in a non-intrusive way. For myself, notifications would be more of a distraction, which is not really helpful, considering I spend most of my time in areas (practice, lessons & translations) where concentration is essential.