Reducing notification frequency I would like to find a way to reduce the global number of notification sounds my phone (4.0) plays, setting a maximum number of plays per minute to avoid multiple applications sending a bunch of noisy messages.

Is there a way to do this?
Not really, no. It's generally up to each individual app to control how often it checks for updates and raises notifications. Not all apps allow you to control that (except, of course, for turning off notifications for that app altogether.)