Probably the most wanted and requested feature is now already available.
The new notification management mechanism allows:

1. Notification contact assignment per check.
2. Specification of the time of the day you wish to receive an alert on.
3. Specification of the week days you wish to receive an alert on.
4. Specification of certain range during the week to receive an alert on.
5. Number of successive failures before an alert will be sent.
6. Selection of locations you wish the failures come from to receive an alert.

To be compliant with an old notification mechanism all your checks are currently set to be sent to your all active and confirmed contacts. You can change that by clicking on the Notification Rules button in the edit part of the External Monitor modules or the edit part of the corresponding contact in the Contact module.
Additional features will be available very soon.