To prevent trashing with many notifications, there are three strategies:

- disable notifications, to the operations, re-enable the notifications.
  this has the disadavantage that you might not know what notifications to 
  send when they are re-enabled. One solution could be to spool them,
  and at re-enable, merge the duplicates and send out the minimum.
- have coarse grained operations, operating on large sets and sending out 
  only one notification at the end.
- Have fine grained modification routines with an option notify that allows
  to decide when to send the notification and when not to.
- Have the model be a centralizer of the notification delivery, but have notifyObserver called
  externally. 
- have a smart signal that can be put in a "trasaction on" mode, and accumulates the
  notifications, and then release the notification when a "commit" is issued