As of version 0.6.0, cake can provide notifications for various events using bake.notify. Currently this is used for cake autotest and supports Growl notifications, but you can use it in your own tasks too, and patches are welcome to add support for other notification systems.
To enable growl notifications, you need to be running OS X, and you need growlnotify installed. You can install it with:
Cake will run you tests whenever a file is changed and use growl to notify you of any exceptions or failures. Cake will also notify you with "All tests passed" when you fix tests that were previously broken.
You can disable notifications by adding the following to ~/.cake/config
# i don't want any awesome notifications, ok?
notifications.disable = true