Yesterday I took a look at the interesting research - Notifications and Awareness: A Field Study of Alert Usage and Preferences.

The aim was to discover the influence of the desktop (Email) notifications on the productivity.

As I undestood the conclusion is that users are able to determine if an notification is urgent and needs an immediate response.

So if user is working on an ongoing task which requires full concentration, in most cases he\she will decide to put notification aside and will continue his\her work.