After my shot with that script back fired a couple of days ago I needed a solution that worked. I remembered that there was a function that might work. I only tried this for the tasks list.
Open your tasks list, click on "List Settings", head over to the "Adcanced settings". You will find "E-Mail Notification" there.
When you click on "Yes", the assigned user will get an Email if something changes in his task, except if it's the description field. And of course he get's an email that a task was assigned to him.